Signal transmission using plurality of aps in wireless lan system

ABSTRACT

A method performed in a wireless local area network (LAN) system is presented. Particularly, a first type access point (AP) #1 can receive a trigger frame from a second type AP. The first type AP #1 can transmit a null data packet (NDP) request frame to a first station (STA). The first type AP #1 can receive a first NDP frame from the first STA, and receive a second NDP frame from a second STA. The first type AP #1 can receive a feedback request frame from the second type AP. The first type AP #1 can transmit an NDP feedback frame to the second type AP on the basis of the first and second NDP frames.

BACKGROUND Field of the Disclosure

The present specification relates to a method of performing a sounding procedure in a wireless LAN system in which a plurality of access points (APs) exist and performing signal transmission using the plurality of APs.

Related Art

A wireless local area network (WLAN) has been enhanced in various ways. For example, the IEEE 802.11ax standard has proposed an enhanced communication environment by using orthogonal frequency division multiple access (OFDMA) and downlink multi-user multiple input multiple output (DL MU MIMO) schemes.

The present specification proposes a technical feature that can be utilized in a new communication standard. For example, the new communication standard may be an extreme high throughput (EHT) standard which is currently being discussed. The EHT standard may use an increased bandwidth, an enhanced PHY layer protocol data unit (PPDU) structure, an enhanced sequence, a hybrid automatic repeat request (HARD) scheme, or the like, which is newly proposed. The EHT standard may be called the IEEE 802.11be standard.

SUMMARY

A method performed in a wireless local area network (WLAN) system according to various embodiments relates to a technical feature in which a first type access point (AP) performs a sounding procedure and performs signal transmission using a plurality of APs. For example, the first type Access Point (AP) #1 may receive a trigger frame from the second type AP. The first type AP #1 may transmit a Null Data Packet (NDP) request frame to a first station (STA). The first type AP #1 may receive a first NDP frame from the first STA and a second NDP frame from the second STA. The first type AP #1 may receive a feedback request frame from the second type AP. The first type AP #1 may transmit an NDP feedback frame to the second type AP based on the first and second NDP frames.

According to the embodiment proposed in this specification, data may be transmitted to STAs through a suitable slave AP in a WLAN environment in which a plurality of APs exist. Also, the sounding procedure can be performed quickly, and more data can be transmitted faster because the plurality of APs are used.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an example of a transmitting apparatus and/or receiving apparatus of the present specification.

FIG. 2 is a conceptual view illustrating the structure of a wireless local area network (WLAN).

FIG. 3 illustrates a general link setup process.

FIG. 4 illustrates an example of a PPDU used in an IEEE standard.

FIG. 5 illustrates a layout of resource units (RUs) used in a band of 20 MHz.

FIG. 6 illustrates a layout of RUs used in a band of 40 MHz.

FIG. 7 illustrates a layout of RUs used in a band of 80 MHz.

FIG. 8 illustrates a structure of an HE-SIG-B field.

FIG. 9 illustrates an example in which a plurality of user STAs are allocated to the same RU through a MU-MIMO scheme.

FIG. 10 illustrates an operation based on UL-MU.

FIG. 11 illustrates an example of a trigger frame.

FIG. 12 illustrates an example of a common information field of a trigger frame.

FIG. 13 illustrates an example of a subfield included in a per user information field.

FIG. 14 describes a technical feature of the UORA scheme.

FIG. 15 illustrates an example of a channel used/supported/defined within a 2.4 GHz band.

FIG. 16 illustrates an example of a channel used/supported/defined within a 5 GHz band.

FIG. 17 illustrates an example of a channel used/supported/defined within a 6 GHz band.

FIG. 18 illustrates an example of a PPDU used in the present specification.

FIG. 19 illustrates an example of a modified transmission device and/or receiving device of the present specification.

FIG. 20 shows an example of activating distributed MIMO transmission (e.g., joint transmission).

FIG. 21 is a diagram illustrating multi-AP coordination.

FIG. 22 shows an example of a null steering operation for interference avoidance.

FIG. 23 shows an example in which AP coordination and interference are controlled.

FIG. 24 shows interference nulling and distributed joint beamforming.

FIG. 25 shows an example of coordinated beamforming.

FIG. 26 is a diagram for explaining C-OFDMA.

FIG. 27 shows an example of joint transmission (e.g., distributed MIMO).

FIG. 28 shows an example of performing joint transmission through the M-AP and the S-AP.

FIG. 29 shows an example of a network configured with multiple APs.

FIG. 30 is a diagram illustrating an example of a method in which a plurality of APs perform joint transmission to a plurality of STAs.

FIG. 31 shows an example of a network configured with multiple APs.

FIG. 32 is a diagram illustrating an example of a method for a plurality of APs to perform multi-AP transmission (MAP) to an STA.

FIG. 33 is a diagram illustrating an example of a method for a plurality of APs to perform multi-AP transmission to an STA.

FIG. 34 is a flowchart illustrating a procedure for performing multi-AP transmission in the S-AP based on the present embodiment.

FIG. 35 is a flowchart illustrating a procedure for performing Multi-AP transmission in an STA according to the present embodiment.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

In the present specification, “A or B” may mean “only A”, “only B” or “both A and B”. In other words, in the present specification, “A or B” may be interpreted as “A and/or B”. For example, in the present specification, “A, B, or C” may mean “only A”, “only B”, “only C”, or “any combination of A, B, C”.

A slash (/) or comma used in the present specification may mean “and/or”. For example, “A/B” may mean “A and/or B”. Accordingly, “A/B” may mean “only A”, “only B”, or “both A and B”. For example, “A, B, C” may mean “A, B, or C”.

In the present specification, “at least one of A and B” may mean “only A”, “only B”, or “both A and B”. In addition, in the present specification, the expression “at least one of A or B” or “at least one of A and/or B” may be interpreted as “at least one of A and B”.

In addition, in the present specification, “at least one of A, B, and C” may mean “only A”, “only B”, “only C”, or “any combination of A, B, and C”. In addition, “at least one of A, B, or C” or “at least one of A, B, and/or C” may mean “at least one of A, B, and C”.

In addition, a parenthesis used in the present specification may mean “for example”. Specifically, when indicated as “control information (EHT-signal)”, it may mean that “EHT-signal” is proposed as an example of the “control information”. In other words, the “control information” of the present specification is not limited to “EHT-signal”, and “EHT-signal” may be proposed as an example of the “control information”. In addition, when indicated as “control information (i.e., EHT-signal)”, it may also mean that “EHT-signal” is proposed as an example of the “control information”.

Technical features described individually in one figure in the present specification may be individually implemented, or may be simultaneously implemented.

The following example of the present specification may be applied to various wireless communication systems. For example, the following example of the present specification may be applied to a wireless local area network (WLAN) system. For example, the present specification may be applied to the IEEE 802.11a/g/n/ac standard or the IEEE 802.11ax standard. In addition, the present specification may also be applied to the newly proposed EHT standard or IEEE 802.11be standard. In addition, the example of the present specification may also be applied to a new WLAN standard enhanced from the EHT standard or the IEEE 802.11be standard. In addition, the example of the present specification may be applied to a mobile communication system. For example, it may be applied to a mobile communication system based on long term evolution (LTE) depending on a 3rd generation partnership project (3GPP) standard and based on evolution of the LTE. In addition, the example of the present specification may be applied to a communication system of a 5G NR standard based on the 3GPP standard.

Hereinafter, in order to describe a technical feature of the present specification, a technical feature applicable to the present specification will be described.

FIG. 1 shows an example of a transmitting apparatus and/or receiving apparatus of the present specification.

In the example of FIG. 1, various technical features described below may be performed. FIG. 1 relates to at least one station (STA). For example, STAs 110 and 120 of the present specification may also be called in various terms such as a mobile terminal, a wireless device, a wireless transmit/receive unit (WTRU), a user equipment (UE), a mobile station (MS), a mobile subscriber unit, or simply a user. The STAs 110 and 120 of the present specification may also be called in various terms such as a network, a base station, a node-B, an access point (AP), a repeater, a router, a relay, or the like. The STAs 110 and 120 of the present specification may also be referred to as various names such as a receiving apparatus, a transmitting apparatus, a receiving STA, a transmitting STA, a receiving device, a transmitting device, or the like.

For example, the STAs 110 and 120 may serve as an AP or a non-AP. That is, the STAs 110 and 120 of the present specification may serve as the AP and/or the non-AP. In The STAs 110 and 120 of the present specification may support various communication standards together in addition to the IEEE 802.11 standard. For example, a communication standard (e.g., LTE, LTE-A, 5G NR standard) or the like based on the 3GPP standard may be supported. In addition, the STA of the present specification may be implemented as various devices such as a mobile phone, a vehicle, a personal computer, or the like. In addition, the STA of the present specification may support communication for various communication services such as voice calls, video calls, data communication, and self-driving (autonomous-driving), or the like.

The STAs 110 and 120 of the present specification may include a medium access control (MAC) conforming to the IEEE 802.11 standard and a physical layer interface for a radio medium.

The STAs 110 and 120 will be described below with reference to a sub-figure (a) of FIG. 1.

The first STA 110 may include a processor 111, a memory 112, and a transceiver 113. The illustrated process, memory, and transceiver may be implemented individually as separate chips, or at least two blocks/functions may be implemented through a single chip.

The transceiver 113 of the first STA performs a signal transmission/reception operation. Specifically, an IEEE 802.11 packet (e.g., IEEE 802.11a/b/g/n/ac/ax/be, etc.) may be transmitted/received.

For example, the first STA 110 may perform an operation intended by an AP. For example, the processor 111 of the AP may receive a signal through the transceiver 113, process a reception (RX) signal, generate a transmission (TX) signal, and provide control for signal transmission. The memory 112 of the AP may store a signal (e.g., RX signal) received through the transceiver 113, and may store a signal (e.g., TX signal) to be transmitted through the transceiver.

For example, the second STA 120 may perform an operation intended by a non-AP STA. For example, a transceiver 123 of a non-AP performs a signal transmission/reception operation. Specifically, an IEEE 802.11 packet (e.g., IEEE 802.11a/b/g/n/ac/ax/be packet, etc.) may be transmitted/received.

For example, a processor 121 of the non-AP STA may receive a signal through the transceiver 123, process an RX signal, generate a TX signal, and provide control for signal transmission. A memory 122 of the non-AP STA may store a signal (e.g., RX signal) received through the transceiver 123, and may store a signal (e.g., TX signal) to be transmitted through the transceiver.

For example, an operation of a device indicated as an AP in the specification described below may be performed in the first STA 110 or the second STA 120. For example, if the first STA 110 is the AP, the operation of the device indicated as the AP may be controlled by the processor 111 of the first STA 110, and a related signal may be transmitted or received through the transceiver 113 controlled by the processor 111 of the first STA 110. In addition, control information related to the operation of the AP or a TX/RX signal of the AP may be stored in the memory 112 of the first STA 110. In addition, if the second STA 120 is the AP, the operation of the device indicated as the AP may be controlled by the processor 121 of the second STA 120, and a related signal may be transmitted or received through the transceiver 123 controlled by the processor 121 of the second STA 120. In addition, control information related to the operation of the AP or a TX/RX signal of the AP may be stored in the memory 122 of the second STA 120.

For example, in the specification described below, an operation of a device indicated as a non-AP (or user-STA) may be performed in the first STA 110 or the second STA 120. For example, if the second STA 120 is the non-AP, the operation of the device indicated as the non-AP may be controlled by the processor 121 of the second STA 120, and a related signal may be transmitted or received through the transceiver 123 controlled by the processor 121 of the second STA 120. In addition, control information related to the operation of the non-AP or a TX/RX signal of the non-AP may be stored in the memory 122 of the second STA 120. For example, if the first STA 110 is the non-AP, the operation of the device indicated as the non-AP may be controlled by the processor 111 of the first STA 110, and a related signal may be transmitted or received through the transceiver 113 controlled by the processor 111 of the first STA 110. In addition, control information related to the operation of the non-AP or a TX/RX signal of the non-AP may be stored in the memory 112 of the first STA 110.

In the specification described below, a device called a (transmitting/receiving) STA, a first STA, a second STA, a STA1, a STA2, an AP, a first AP, a second AP, an AP1, an AP2, a (transmitting/receiving) terminal, a (transmitting/receiving) device, a (transmitting/receiving) apparatus, a network, or the like may imply the STAs 110 and 120 of FIG. 1. For example, a device indicated as, without a specific reference numeral, the (transmitting/receiving) STA, the first STA, the second STA, the STA1, the STA2, the AP, the first AP, the second AP, the AP1, the AP2, the (transmitting/receiving) terminal, the (transmitting/receiving) device, the (transmitting/receiving) apparatus, the network, or the like may imply the STAs 110 and 120 of FIG. 1. For example, in the following example, an operation in which various STAs transmit/receive a signal (e.g., a PPDU) may be performed in the transceivers 113 and 123 of FIG. 1. In addition, in the following example, an operation in which various STAs generate a TX/RX signal or perform data processing and computation in advance for the TX/RX signal may be performed in the processors 111 and 121 of FIG. 1. For example, an example of an operation for generating the TX/RX signal or performing the data processing and computation in advance may include: 1) an operation of determining/obtaining/configuring/computing/decoding/encoding bit information of a sub-field (SIG, STF, LTF, Data) included in a PPDU; 2) an operation of determining/configuring/obtaining a time resource or frequency resource (e.g., a subcarrier resource) or the like used for the sub-field (SIG, STF, LTF, Data) included the PPDU; 3) an operation of determining/configuring/obtaining a specific sequence (e.g., a pilot sequence, an STF/LTF sequence, an extra sequence applied to SIG) or the like used for the sub-field (SIG, STF, LTF, Data) field included in the PPDU; 4) a power control operation and/or power saving operation applied for the STA; and 5) an operation related to determining/obtaining/configuring/decoding/encoding or the like of an ACK signal. In addition, in the following example, a variety of information used by various STAs for determining/obtaining/configuring/computing/decoding/decoding a TX/RX signal (e.g., information related to a field/subfield/control field/parameter/power or the like) may be stored in the memories 112 and 122 of FIG. 1.

The aforementioned device/STA of the sub-figure (a) of FIG. 1 may be modified as shown in the sub-figure (b) of FIG. 1. Hereinafter, the STAs 110 and 120 of the present specification will be described based on the sub-figure (b) of FIG. 1.

For example, the transceivers 113 and 123 illustrated in the sub-figure (b) of FIG. 1 may perform the same function as the aforementioned transceiver illustrated in the sub-figure (a) of FIG. 1. For example, processing chips 114 and 124 illustrated in the sub-figure (b) of FIG. 1 may include the processors 111 and 121 and the memories 112 and 122. The processors 111 and 121 and memories 112 and 122 illustrated in the sub-figure (b) of FIG. 1 may perform the same function as the aforementioned processors 111 and 121 and memories 112 and 122 illustrated in the sub-figure (a) of FIG. 1.

A mobile terminal, a wireless device, a wireless transmit/receive unit (WTRU), a user equipment (UE), a mobile station (MS), a mobile subscriber unit, a user, a user STA, a network, a base station, a Node-B, an access point (AP), a repeater, a router, a relay, a receiving unit, a transmitting unit, a receiving STA, a transmitting STA, a receiving device, a transmitting device, a receiving apparatus, and/or a transmitting apparatus, which are described below, may imply the STAs 110 and 120 illustrated in the sub-figure (a)/(b) of FIG. 1, or may imply the processing chips 114 and 124 illustrated in the sub-figure (b) of FIG. 1. That is, a technical feature of the present specification may be performed in the STAs 110 and 120 illustrated in the sub-figure (a)/(b) of FIG. 1, or may be performed only in the processing chips 114 and 124 illustrated in the sub-figure (b) of FIG. 1. For example, a technical feature in which the transmitting STA transmits a control signal may be understood as a technical feature in which a control signal generated in the processors 111 and 121 illustrated in the sub-figure (a)/(b) of FIG. 1 is transmitted through the transceivers 113 and 123 illustrated in the sub-figure (a)/(b) of FIG. 1. Alternatively, the technical feature in which the transmitting STA transmits the control signal may be understood as a technical feature in which the control signal to be transferred to the transceivers 113 and 123 is generated in the processing chips 114 and 124 illustrated in the sub-figure (b) of FIG. 1.

For example, a technical feature in which the receiving STA receives the control signal may be understood as a technical feature in which the control signal is received by means of the transceivers 113 and 123 illustrated in the sub-figure (a) of FIG. 1. Alternatively, the technical feature in which the receiving STA receives the control signal may be understood as the technical feature in which the control signal received in the transceivers 113 and 123 illustrated in the sub-figure (a) of FIG. 1 is obtained by the processors 111 and 121 illustrated in the sub-figure (a) of FIG. 1. Alternatively, the technical feature in which the receiving STA receives the control signal may be understood as the technical feature in which the control signal received in the transceivers 113 and 123 illustrated in the sub-figure (b) of FIG. 1 is obtained by the processing chips 114 and 124 illustrated in the sub-figure (b) of FIG. 1.

Referring to the sub-figure (b) of FIG. 1, software codes 115 and 125 may be included in the memories 112 and 122. The software codes 115 and 126 may include instructions for controlling an operation of the processors 111 and 121. The software codes 115 and 125 may be included as various programming languages.

The processors 111 and 121 or processing chips 114 and 124 of FIG. 1 may include an application-specific integrated circuit (ASIC), other chipsets, a logic circuit and/or a data processing device. The processor may be an application processor (AP). For example, the processors 111 and 121 or processing chips 114 and 124 of FIG. 1 may include at least one of a digital signal processor (DSP), a central processing unit (CPU), a graphics processing unit (GPU), and a modulator and demodulator (modem). For example, the processors 111 and 121 or processing chips 114 and 124 of FIG. 1 may be SNAPDRAGON™ series of processors made by Qualcomm®, EXYNOS™ series of processors made by Samsung®, A series of processors made by Apple®, HELIO™ series of processors made by MediaTek®, ATOM™ series of processors made by Intel® or processors enhanced from these processors.

In the present specification, an uplink may imply a link for communication from a non-AP STA to an SP STA, and an uplink PPDU/packet/signal or the like may be transmitted through the uplink. In addition, in the present specification, a downlink may imply a link for communication from the AP STA to the non-AP STA, and a downlink PPDU/packet/signal or the like may be transmitted through the downlink.

FIG. 2 is a conceptual view illustrating the structure of a wireless local area network (WLAN).

An upper part of FIG. 2 illustrates the structure of an infrastructure basic service set (BSS) of institute of electrical and electronic engineers (IEEE) 802.11.

Referring the upper part of FIG. 2, the wireless LAN system may include one or more infrastructure BSSs 200 and 205 (hereinafter, referred to as BSS). The BSSs 200 and 205 as a set of an AP and a STA such as an access point (AP) 225 and a station (STA1) 200-1 which are successfully synchronized to communicate with each other are not concepts indicating a specific region. The BSS 205 may include one or more STAs 205-1 and 205-2 which may be joined to one AP 230.

The BSS may include at least one STA, APs providing a distribution service, and a distribution system (DS) 210 connecting multiple APs.

The distribution system 210 may implement an extended service set (ESS) 240 extended by connecting the multiple BSSs 200 and 205. The ESS 240 may be used as a term indicating one network configured by connecting one or more APs 225 or 230 through the distribution system 210. The AP included in one ESS 240 may have the same service set identification (SSID).

A portal 220 may serve as a bridge which connects the wireless LAN network (IEEE 802.11) and another network (e.g., 802.X).

In the BSS illustrated in the upper part of FIG. 2, a network between the APs 225 and 230 and a network between the APs 225 and 230 and the STAs 200-1, 205-1, and 205-2 may be implemented. However, the network is configured even between the STAs without the APs 225 and 230 to perform communication. A network in which the communication is performed by configuring the network even between the STAs without the APs 225 and 230 is defined as an Ad-Hoc network or an independent basic service set (IBSS).

A lower part of FIG. 2 illustrates a conceptual view illustrating the IBSS.

Referring to the lower part of FIG. 2, the IBSS is a BSS that operates in an Ad-Hoc mode. Since the IBSS does not include the access point (AP), a centralized management entity that performs a management function at the center does not exist. That is, in the IBSS, STAs 250-1, 250-2, 250-3, 255-4, and 255-5 are managed by a distributed manner. In the IBSS, all STAs 250-1, 250-2, 250-3, 255-4, and 255-5 may be constituted by movable STAs and are not permitted to access the DS to constitute a self-contained network.

FIG. 3 illustrates a general link setup process.

In S310, a STA may perform a network discovery operation. The network discovery operation may include a scanning operation of the STA. That is, to access a network, the STA needs to discover a participating network. The STA needs to identify a compatible network before participating in a wireless network, and a process of identifying a network present in a particular area is referred to as scanning. Scanning methods include active scanning and passive scanning.

FIG. 3 illustrates a network discovery operation including an active scanning process. In active scanning, a STA performing scanning transmits a probe request frame and waits for a response to the probe request frame in order to identify which AP is present around while moving to channels. A responder transmits a probe response frame as a response to the probe request frame to the STA having transmitted the probe request frame. Here, the responder may be a STA that transmits the last beacon frame in a BSS of a channel being scanned. In the BSS, since an AP transmits a beacon frame, the AP is the responder. In an IBSS, since STAs in the IBSS transmit a beacon frame in turns, the responder is not fixed. For example, when the STA transmits a probe request frame via channel 1 and receives a probe response frame via channel 1, the STA may store B SS-related information included in the received probe response frame, may move to the next channel (e.g., channel 2), and may perform scanning (e.g., transmits a probe request and receives a probe response via channel 2) by the same method.

Although not shown in FIG. 3, scanning may be performed by a passive scanning method. In passive scanning, a STA performing scanning may wait for a beacon frame while moving to channels. A beacon frame is one of management frames in IEEE 802.11 and is periodically transmitted to indicate the presence of a wireless network and to enable the STA performing scanning to find the wireless network and to participate in the wireless network. In a BSS, an AP serves to periodically transmit a beacon frame. In an IBSS, STAs in the IBSS transmit a beacon frame in turns. Upon receiving the beacon frame, the STA performing scanning stores information about a BSS included in the beacon frame and records beacon frame information in each channel while moving to another channel. The STA having received the beacon frame may store BSS-related information included in the received beacon frame, may move to the next channel, and may perform scanning in the next channel by the same method.

After discovering the network, the STA may perform an authentication process in S320. The authentication process may be referred to as a first authentication process to be clearly distinguished from the following security setup operation in S340. The authentication process in S320 may include a process in which the STA transmits an authentication request frame to the AP and the AP transmits an authentication response frame to the STA in response. The authentication frames used for an authentication request/response are management frames.

The authentication frames may include information about an authentication algorithm number, an authentication transaction sequence number, a status code, a challenge text, a robust security network (RSN), and a finite cyclic group.

The STA may transmit the authentication request frame to the AP. The AP may determine whether to allow the authentication of the STA based on the information included in the received authentication request frame. The AP may provide the authentication processing result to the STA via the authentication response frame.

When the STA is successfully authenticated, the STA may perform an association process in S330. The association process includes a process in which the STA transmits an association request frame to the AP and the AP transmits an association response frame to the STA in response. The association request frame may include, for example, information about various capabilities, a beacon listen interval, a service set identifier (SSID), a supported rate, a supported channel, RSN, a mobility domain, a supported operating class, a traffic indication map (TIM) broadcast request, and an interworking service capability. The association response frame may include, for example, information about various capabilities, a status code, an association ID (AID), a supported rate, an enhanced distributed channel access (EDCA) parameter set, a received channel power indicator (RCPI), a received signal-to-noise indicator (RSNI), a mobility domain, a timeout interval (association comeback time), an overlapping BSS scanning parameter, a TIM broadcast response, and a QoS map.

In S340, the STA may perform a security setup process. The security setup process in S340 may include a process of setting up a private key through four-way handshaking, for example, through an extensible authentication protocol over LAN (EAPOL) frame.

FIG. 4 illustrates an example of a PPDU used in an IEEE standard.

As illustrated, various types of PHY protocol data units (PPDUs) are used in IEEE a/g/n/ac standards. Specifically, a LTF and a STF include a training signal, a SIG-A and a SIG-B include control information for a receiving STA, and a data field includes user data corresponding to a PSDU (MAC PDU/aggregated MAC PDU).

FIG. 4 also includes an example of an HE PPDU according to IEEE 802.11ax. The HE PPDU according to FIG. 4 is an illustrative PPDU for multiple users. An HE-SIG-B may be included only in a PPDU for multiple users, and an HE-SIG-B may be omitted in a PPDU for a single user.

As illustrated in FIG. 4, the HE-PPDU for multiple users (MUs) may include a legacy-short training field (L-STF), a legacy-long training field (L-LTF), a legacy-signal (L-SIG), a high efficiency-signal A (HE-SIG A), a high efficiency-signal-B (HE-SIG B), a high efficiency-short training field (HE-STF), a high efficiency-long training field (HE-LTF), a data field (alternatively, an MAC payload), and a packet extension (PE) field. The respective fields may be transmitted for illustrated time periods (i.e., 4 or 8 μs).

Hereinafter, a resource unit (RU) used for a PPDU is described. An RU may include a plurality of subcarriers (or tones). An RU may be used to transmit a signal to a plurality of STAs according to OFDMA. Further, an RU may also be defined to transmit a signal to one STA. An RU may be used for an STF, an LTF, a data field, or the like.

FIG. 5 illustrates a layout of resource units (RUs) used in a band of 20 MHz.

As illustrated in FIG. 5, resource units (RUs) corresponding to different numbers of tones (i.e., subcarriers) may be used to form some fields of an HE-PPDU. For example, resources may be allocated in illustrated RUs for an HE-STF, an HE-LTF, and a data field.

As illustrated in the uppermost part of FIG. 5, a 26-unit (i.e., a unit corresponding to 26 tones) may be disposed. Six tones may be used for a guard band in the leftmost band of the 20 MHz band, and five tones may be used for a guard band in the rightmost band of the 20 MHz band. Further, seven DC tones may be inserted in a center band, that is, a DC band, and a 26-unit corresponding to 13 tones on each of the left and right sides of the DC band may be disposed. A 26-unit, a 52-unit, and a 106-unit may be allocated to other bands. Each unit may be allocated for a receiving STA, that is, a user.

The layout of the RUs in FIG. 5 may be used not only for a multiple users (MUs) but also for a single user (SU), in which case one 242-unit may be used and three DC tones may be inserted as illustrated in the lowermost part of FIG. 5.

Although FIG. 5 proposes RUs having various sizes, that is, a 26-RU, a 52-RU, a 106-RU, and a 242-RU, specific sizes of RUs may be extended or increased. Therefore, the present embodiment is not limited to the specific size of each RU (i.e., the number of corresponding tones).

FIG. 6 illustrates a layout of RUs used in a band of 40 MHz.

Similarly to FIG. 5 in which RUs having various sizes are used, a 26-RU, a 52-RU, a 106-RU, a 242-RU, a 484-RU, and the like may be used in an example of FIG. 6. Further, five DC tones may be inserted in a center frequency, 12 tones may be used for a guard band in the leftmost band of the 40 MHz band, and 11 tones may be used for a guard band in the rightmost band of the 40 MHz band.

As illustrated in FIG. 6, when the layout of the RUs is used for a single user, a 484-RU may be used. The specific number of RUs may be changed similarly to FIG. 5.

FIG. 7 illustrates a layout of RUs used in a band of 80 MHz.

Similarly to FIG. 5 and FIG. 6 in which RUs having various sizes are used, a 26-RU, a 52-RU, a 106-RU, a 242-RU, a 484-RU, a 996-RU, and the like may be used in an example of FIG. 7. Further, seven DC tones may be inserted in the center frequency, 12 tones may be used for a guard band in the leftmost band of the 80 MHz band, and 11 tones may be used for a guard band in the rightmost band of the 80 MHz band. In addition, a 26-RU corresponding to 13 tones on each of the left and right sides of the DC band may be used.

As illustrated in FIG. 7, when the layout of the RUs is used for a single user, a 996-RU may be used, in which case five DC tones may be inserted.

In the meantime, the fact that the specific number of RUs can be changed is the same as those of FIGS. 5 and 6.

The RU arrangement (i.e., RU location) shown in FIGS. 5 to 7 can be applied to a new wireless LAN system (e.g. EHT system) as it is. Meanwhile, for the 160 MHz band supported by the new WLAN system, the RU arrangement for 80 MHz (i.e., an example of FIG. 7) may be repeated twice, or the RU arrangement for the 40 MHz (i.e., an example of FIG. 6) may be repeated 4 times. In addition, when the EHT PPDU is configured for the 320 MHz band, the arrangement of the RU for 80 MHz (i.e., an example of FIG. 7) may be repeated 4 times or the arrangement of the RU for 40 MHz (i.e., an example of FIG. 6) may be repeated 8 times.

One RU of the present specification may be allocated for a single STA (e.g., a single non-AP STA). Alternatively, a plurality of RUs may be allocated for one STA (e.g., a non-AP STA).

The RU described in the present specification may be used in uplink (UL) communication and downlink (DL) communication. For example, when UL-MU communication which is solicited by a trigger frame is performed, a transmitting STA (e.g., an AP) may allocate a first RU (e.g., 26/52/106/242-RU, etc.) to a first STA through the trigger frame, and may allocate a second RU (e.g., 26/52/106/242-RU, etc.) to a second STA. Thereafter, the first STA may transmit a first trigger-based PPDU based on the first RU, and the second STA may transmit a second trigger-based PPDU based on the second RU. The first/second trigger-based PPDU is transmitted to the AP at the same (or overlapped) time period.

For example, when a DL MU PPDU is configured, the transmitting STA (e.g., AP) may allocate the first RU (e.g., 26/52/106/242-RU. etc.) to the first STA, and may allocate the second RU (e.g., 26/52/106/242-RU, etc.) to the second STA. That is, the transmitting STA (e.g., AP) may transmit HE-STF, HE-LTF, and Data fields for the first STA through the first RU in one MU PPDU, and may transmit HE-STF, HE-LTF, and Data fields for the second STA through the second RU.

Information related to a layout of the RU may be signaled through HE-SIG-B.

FIG. 8 illustrates a structure of an HE-SIG-B field.

As illustrated, an HE-SIG-B field 810 includes a common field 820 and a user-specific field 830. The common field 820 may include information commonly applied to all users (i.e., user STAs) which receive SIG-B. The user-specific field 830 may be called a user-specific control field. When the SIG-B is transferred to a plurality of users, the user-specific field 830 may be applied only any one of the plurality of users.

As illustrated in FIG. 8, the common field 820 and the user-specific field 830 may be separately encoded.

The common field 820 may include RU allocation information of N*8 bits. For example, the RU allocation information may include information related to a location of an RU. For example, when a 20 MHz channel is used as shown in FIG. 5, the RU allocation information may include information related to a specific frequency band to which a specific RU (26-RU/52-RU/106-RU) is arranged.

An example of a case in which the RU allocation information consists of 8 bits is as follows.

TABLE 1 8 bits indices (B7 B6 B5 B4 Number B3 B2 B1 B0) #1 #2 #3 #4 #5 #6 #7 #8 #9 of entries 00000000 26 26 26 26 26 26 26 26 26 1 00000001 26 26 26 26 26 26 26 52 1 00000010 26 26 26 26 26 52 26 26 1 00000011 26 26 26 26 26 52 52 1 00000100 26 26 52 26 26 26 26 26 1 00000101 26 26 52 26 26 26 52 1 00000110 26 26 52 26 52 26 26 1 00000111 26 26 52 26 52 52 1 00001000 52 26 26 26 26 26 26 26 1

As shown the example of FIG. 5, up to nine 26-RUs may be allocated to the 20 MHz channel. When the RU allocation information of the common field 820 is set to “00000000” as shown in Table 1, the nine 26-RUs may be allocated to a corresponding channel (i.e., 20 MHz). In addition, when the RU allocation information of the common field 820 is set to “00000001” as shown in Table 1, seven 26-RUs and one 52-RU are arranged in a corresponding channel. That is, in the example of FIG. 5, the 52-RU may be allocated to the rightmost side, and the seven 26-RUs may be allocated to the left thereof.

The example of Table 1 shows only some of RU locations capable of displaying the RU allocation information.

For example, the RU allocation information may include an example of Table 2 below.

TABLE 2 8 bits indices (B7 B6 B5 B4 Number B3 B2 B1 B0) #1 #2 #3 #4 #5 #6 #7 #8 #9 of entries 01000y₂y₁y₀ 106 26 26 26 26 26 8 01001y₂y₁y₀ 106 26 26 26 52 8

“01000y2y1y0” relates to an example in which a 106-RU is allocated to the leftmost side of the 20 MHz channel, and five 26-RUs are allocated to the right side thereof. In this case, a plurality of STAs (e.g., user-STAs) may be allocated to the 106-RU, based on a MU-MIMO scheme. Specifically, up to 8 STAs (e.g., user-STAs) may be allocated to the 106-RU, and the number of STAs (e.g., user-STAs) allocated to the 106-RU is determined based on 3-bit information (y2y1y0). For example, when the 3-bit information (y2y1y0) is set to N, the number of STAs (e.g., user-STAs) allocated to the 106-RU based on the MU-MIMO scheme may be N+1.

In general, a plurality of STAs (e.g., user STAs) different from each other may be allocated to a plurality of RUs. However, the plurality of STAs (e.g., user STAs) may be allocated to one or more RUs having at least a specific size (e.g., 106 subcarriers), based on the MU-MIMO scheme.

As shown in FIG. 8, the user-specific field 830 may include a plurality of user fields. As described above, the number of STAs (e.g., user STAs) allocated to a specific channel may be determined based on the RU allocation information of the common field 820. For example, when the RU allocation information of the common field 820 is “00000000”, one user STA may be allocated to each of nine 26-RUs (e.g., nine user STAs may be allocated). That is, up to 9 user STAs may be allocated to a specific channel through an OFDMA scheme. In other words, up to 9 user STAs may be allocated to a specific channel through a non-MU-MIMO scheme.

For example, when RU allocation is set to “01000y2y1y0”, a plurality of STAs may be allocated to the 106-RU arranged at the leftmost side through the MU-MIMO scheme, and five user STAs may be allocated to five 26-RUs arranged to the right side thereof through the non-MU MIMO scheme. This case is specified through an example of FIG. 9.

FIG. 9 illustrates an example in which a plurality of user STAs are allocated to the same RU through a MU-MIMO scheme.

For example, when RU allocation is set to “01000010” as shown in FIG. 9, a 106-RU may be allocated to the leftmost side of a specific channel, and five 26-RUs may be allocated to the right side thereof. In addition, three user STAs may be allocated to the 106-RU through the MU-MIMO scheme. As a result, since eight user STAs are allocated, the user-specific field 830 of HE-SIG-B may include eight user fields.

The eight user fields may be expressed in the order shown in FIG. 9. In addition, as shown in FIG. 8, two user fields may be implemented with one user block field.

The user fields shown in FIG. 8 and FIG. 9 may be configured based on two formats. That is, a user field related to a MU-MIMO scheme may be configured in a first format, and a user field related to a non-MIMO scheme may be configured in a second format. Referring to the example of FIG. 9, a user field 1 to a user field 3 may be based on the first format, and a user field 4 to a user field 8 may be based on the second format. The first format or the second format may include bit information of the same length (e.g., 21 bits).

Each user field may have the same size (e.g., 21 bits). For example, the user field of the first format (the first of the MU-MIMO scheme) may be configured as follows.

For example, a first bit (i.e., B0-B10) in the user field (i.e., 21 bits) may include identification information (e.g., STA-ID, partial AID, etc.) of a user STA to which a corresponding user field is allocated. In addition, a second bit (i.e., B11-B14) in the user field (i.e., 21 bits) may include information related to a spatial configuration. Specifically, an example of the second bit (i.e., B11-B14) may be as shown in Table 3 and Table 4 below.

TABLE 3 N_(STS) N_(STS) N_(STS) N_(STS) N_(STS) N_(STS) N_(STS) N_(STS) Total Number N_(user) B3 . . . B0 [1] [2] [3] [4] [5] [6] [7] [8] N_(STS) of entries 2 0000-0011 1-4 1 2-5 10 0100-0110 2-4 2 4-6 0111-1000 3-4 3 6-7 1001 4 4 8 3 0000-0011 1-4 1 1 3-6 13 0100-0110 2-4 2 1 5-7 0111-1000 3-4 3 1 7-8 1001-1011 2-4 2 2 6-8 1100 3 3 2 8 4 0000-0011 1-4 1 1 1 4-7 11 0100-0110 2-4 2 1 1 6-8 0111 3 3 1 1 8 1000-1001 2-3 2 2 1 7-8 1010 2 2 2 2 8

TABLE 4 N_(STS) N_(STS) N_(STS) N_(STS) N_(STS) N_(STS) N_(STS) N_(STS) Total Number N_(user) B3 . . . B0 [1] [2] [3] [4] [5] [6] [7] [8] N_(STS) of entries 5 0000-0011 1-4 1 1 1 1 5-8 7 0100-0101 2-3 2 1 1 1 7-8 0110 2 2 2 1 1 8 6 0000-0010 1-3 1 1 1 1 1 6-8 4 0011 2 2 1 1 1 1 8 7 0000-0001 1-2 1 1 1 1 1 1 7-8 2 8 0000 1 1 1 1 1 1 1 1 8 1

As shown in Table 3 and/or Table 4, the second bit (e.g., B11-B14) may include information related to the number of spatial streams allocated to the plurality of user STAs which are allocated based on the MU-MIMO scheme. For example, when three user STAs are allocated to the 106-RU based on the MU-MIMO scheme as shown in FIG. 9, N_user is set to “3”. Therefore, values of N_STS[1], N_STS[2], and N_STS[3] may be determined as shown in Table 3. For example, when a values of the second bit (B11-B14) is “0011”, it may be set to N_STS[1]=4, N_STS[2]=1, N_STS[3]=1. That is, in the example of FIG. 9, four spatial streams may be allocated to the user field 1, one spatial stream may be allocated to the user field 1, and one spatial stream may be allocated to the user field 3.

As shown in the example of Table 3 and/or Table 4, information (i.e., the second bit, B11-B14) related to the number of spatial streams for the user STA may consist of 4 bits. In addition, the information (i.e., the second bit, B11-B14) on the number of spatial streams for the user STA may support up to eight spatial streams. In addition, the information (i.e., the second bit, B11-B14) on the number of spatial streams for the user STA may support up to four spatial streams for one user STA.

In addition, a third bit (i.e., B15-18) in the user field (i.e., 21 bits) may include modulation and coding scheme (MCS) information. The MCS information may be applied to a data field in a PPDU including corresponding SIG-B.

An MCS, MCS information, an MCS index, an MCS field, or the like used in the present specification may be indicated by an index value. For example, the MCS information may be indicated by an index 0 to an index 11. The MCS information may include information related to a constellation modulation type (e.g., BPSK, QPSK, 16-QAM, 64-QAM, 256-QAM, 1024-QAM, etc.) and information related to a coding rate (e.g., 1/2, 2/3, 3/4, 5/6e, etc.). Information related to a channel coding type (e.g., LCC or LDPC) may be excluded in the MCS information.

In addition, a fourth bit (i.e., B19) in the user field (i.e., 21 bits) may be a reserved field.

In addition, a fifth bit (i.e., B20) in the user field (i.e., 21 bits) may include information related to a coding type (e.g., BCC or LDPC). That is, the fifth bit (i.e., B20) may include information related to a type (e.g., BCC or LDPC) of channel coding applied to the data field in the PPDU including the corresponding SIG-B.

The aforementioned example relates to the user field of the first format (the format of the MU-MIMO scheme). An example of the user field of the second format (the format of the non-MU-MIMO scheme) is as follows.

A first bit (e.g., B0-B10) in the user field of the second format may include identification information of a user STA. In addition, a second bit (e.g., B11-B13) in the user field of the second format may include information related to the number of spatial streams applied to a corresponding RU. In addition, a third bit (e.g., B14) in the user field of the second format may include information related to whether a beamforming steering matrix is applied. A fourth bit (e.g., B15-B18) in the user field of the second format may include modulation and coding scheme (MCS) information. In addition, a fifth bit (e.g., B19) in the user field of the second format may include information related to whether dual carrier modulation (DCM) is applied. In addition, a sixth bit (i.e., B20) in the user field of the second format may include information related to a coding type (e.g., BCC or LDPC).

FIG. 10 illustrates an operation based on UL-MU. As illustrated, a transmitting STA (e.g., an AP) may perform channel access through contending (e.g., a backoff operation), and may transmit a trigger frame 1030. That is, the transmitting STA may transmit a PPDU including the trigger frame 1030. Upon receiving the PPDU including the trigger frame, a trigger-based (TB) PPDU is transmitted after a delay corresponding to SIFS.

TB PPDUs 1041 and 1042 may be transmitted at the same time period, and may be transmitted from a plurality of STAs (e.g., user STAs) having AIDs indicated in the trigger frame 1030. An ACK frame 1050 for the TB PPDU may be implemented in various forms.

A specific feature of the trigger frame is described with reference to FIG. 11 to FIG. 13. Even if UL-MU communication is used, an orthogonal frequency division multiple access (OFDMA) scheme or a MU MIMO scheme may be used, and the OFDMA and MU-MIMO schemes may be simultaneously used.

FIG. 11 illustrates an example of a trigger frame. The trigger frame of FIG. 11 allocates a resource for uplink multiple-user (MU) transmission, and may be transmitted, for example, from an AP. The trigger frame may be configured of a MAC frame, and may be included in a PPDU.

Each field shown in FIG. 11 may be partially omitted, and another field may be added. In addition, a length of each field may be changed to be different from that shown in the figure.

A frame control field 1110 of FIG. 11 may include information related to a MAC protocol version and extra additional control information. A duration field 1120 may include time information for NAV configuration or information related to an identifier (e.g., AID) of a STA.

In addition, an RA field 1130 may include address information of a receiving STA of a corresponding trigger frame, and may be optionally omitted. A TA field 1140 may include address information of a STA (e.g., an AP) which transmits the corresponding trigger frame. A common information field 1150 includes common control information applied to the receiving STA which receives the corresponding trigger frame. For example, a field indicating a length of an L-SIG field of an uplink PPDU transmitted in response to the corresponding trigger frame or information for controlling content of an SIG-A field (i.e., HE-SIG-A field) of the uplink PPDU transmitted in response to the corresponding trigger frame may be included. In addition, as common control information, information related to a length of a CP of the uplink PPDU transmitted in response to the corresponding trigger frame or information related to a length of an LTF field may be included.

In addition, per user information fields 1160#1 to 1160#N corresponding to the number of receiving STAs which receive the trigger frame of FIG. 11 are preferably included. The per user information field may also be called an “allocation field”.

In addition, the trigger frame of FIG. 11 may include a padding field 1170 and a frame check sequence field 1180.

Each of the per user information fields 1160#1 to 1160#N shown in FIG. 11 may include a plurality of subfields.

FIG. 12 illustrates an example of a common information field of a trigger frame. A subfield of FIG. 12 may be partially omitted, and an extra subfield may be added. In addition, a length of each subfield illustrated may be changed.

A length field 1210 illustrated has the same value as a length field of an L-SIG field of an uplink PPDU transmitted in response to a corresponding trigger frame, and a length field of the L-SIG field of the uplink PPDU indicates a length of the uplink PPDU. As a result, the length field 1210 of the trigger frame may be used to indicate the length of the corresponding uplink PPDU.

In addition, a cascade identifier field 1220 indicates whether a cascade operation is performed. The cascade operation implies that downlink MU transmission and uplink MU transmission are performed together in the same TXOP. That is, it implies that downlink MU transmission is performed and thereafter uplink MU transmission is performed after a pre-set time (e.g., SIFS). During the cascade operation, only one transmitting device (e.g., AP) may perform downlink communication, and a plurality of transmitting devices (e.g., non-APs) may perform uplink communication.

A CS request field 1230 indicates whether a wireless medium state or an NAV or the like is necessarily considered in a situation where a receiving device which has received a corresponding trigger frame transmits a corresponding uplink PPDU.

An HE-SIG-A information field 1240 may include information for controlling content of an SIG-A field (i.e., HE-SIG-A field) of the uplink PPDU in response to the corresponding trigger frame.

A CP and LTF type field 1250 may include information related to a CP length and LTF length of the uplink PPDU transmitted in response to the corresponding trigger frame. A trigger type field 1260 may indicate a purpose of using the corresponding trigger frame, for example, typical triggering, triggering for beamforming, a request for block ACK/NACK, or the like.

It may be assumed that the trigger type field 1260 of the trigger frame in the present specification indicates a trigger frame of a basic type for typical triggering. For example, the trigger frame of the basic type may be referred to as a basic trigger frame.

FIG. 13 illustrates an example of a subfield included in a per user information field. A user information field 1300 of FIG. 13 may be understood as any one of the per user information fields 1160#1 to 1160#N mentioned above with reference to FIG. 11. A subfield included in the user information field 1300 of FIG. 13 may be partially omitted, and an extra subfield may be added. In addition, a length of each subfield illustrated may be changed.

A user identifier field 1310 of FIG. 13 indicates an identifier of a STA (i.e., receiving STA) corresponding to per user information. An example of the identifier may be the entirety or part of an association identifier (AID) value of the receiving STA.

In addition, an RU allocation field 1320 may be included. That is, when the receiving STA identified through the user identifier field 1310 transmits a TB PPDU in response to the trigger frame, the TB PPDU is transmitted through an RU indicated by the RU allocation field 1320. In this case, the RU indicated by the RU allocation field 1320 may be an RU shown in FIG. 5, FIG. 6, and FIG. 7.

The subfield of FIG. 13 may include a coding type field 1330. The coding type field 1330 may indicate a coding type of the TB PPDU. For example, when BCC coding is applied to the TB PPDU, the coding type field 1330 may be set to ‘1’, and when LDPC coding is applied, the coding type field 1330 may be set to ‘0’.

In addition, the subfield of FIG. 13 may include an MCS field 1340. The MCS field 1340 may indicate an MCS scheme applied to the TB PPDU. For example, when BCC coding is applied to the TB PPDU, the coding type field 1330 may be set to ‘1’, and when LDPC coding is applied, the coding type field 1330 may be set to ‘0’.

Hereinafter, a UL OFDMA-based random access (UORA) scheme will be described.

FIG. 14 describes a technical feature of the UORA scheme.

A transmitting STA (e.g., an AP) may allocate six RU resources through a trigger frame as shown in FIG. 14. Specifically, the AP may allocate a 1st RU resource (AID 0, RU 1), a 2nd RU resource (AID 0, RU 2), a 3rd RU resource (AID 0, RU 3), a 4th RU resource (AID 2045, RU 4), a 5th RU resource (AID 2045, RU 5), and a 6th RU resource (AID 3, RU 6). Information related to the AID 0, AID 3, or AID 2045 may be included, for example, in the user identifier field 1310 of FIG. 13. Information related to the RU 1 to RU 6 may be included, for example, in the RU allocation field 1320 of FIG. 13. AID=0 may imply a UORA resource for an associated STA, and AID=2045 may imply a UORA resource for an un-associated STA. Accordingly, the 1st to 3rd RU resources of FIG. 14 may be used as a UORA resource for the associated STA, the 4th and 5th RU resources of FIG. 14 may be used as a UORA resource for the un-associated STA, and the 6th RU resource of FIG. 14 may be used as a typical resource for UL MU.

In the example of FIG. 14, an OFDMA random access backoff (OBO) of a STA1 is decreased to 0, and the STA1 randomly selects the 2nd RU resource (AID 0, RU 2). In addition, since an OBO counter of a STA2/3 is greater than 0, an uplink resource is not allocated to the STA2/3. In addition, regarding a STA4 in FIG. 14, since an AID (e.g., AID=3) of the STA4 is included in a trigger frame, a resource of the RU 6 is allocated without backoff.

Specifically, since the STA1 of FIG. 14 is an associated STA, the total number of eligible RA RUs for the STA1 is 3 (RU 1, RU 2, and RU 3), and thus the STA1 decreases an OBO counter by 3 so that the OBO counter becomes 0. In addition, since the STA2 of FIG. 14 is an associated STA, the total number of eligible RA RUs for the STA2 is 3 (RU 1, RU 2, and RU 3), and thus the STA2 decreases the OBO counter by 3 but the OBO counter is greater than 0. In addition, since the STA3 of FIG. 14 is an un-associated STA, the total number of eligible RA RUs for the STA3 is 2 (RU 4, RU 5), and thus the STA3 decreases the OBO counter by 2 but the OBO counter is greater than 0.

FIG. 15 illustrates an example of a channel used/supported/defined within a 2.4 GHz band.

The 2.4 GHz band may be called in other terms such as a first band. In addition, the 2.4 GHz band may imply a frequency domain in which channels of which a center frequency is close to 2.4 GHz (e.g., channels of which a center frequency is located within 2.4 to 2.5 GHz) are used/supported/defined.

A plurality of 20 MHz channels may be included in the 2.4 GHz band. 20 MHz within the 2.4 GHz may have a plurality of channel indices (e.g., an index 1 to an index 14). For example, a center frequency of a 20 MHz channel to which a channel index 1 is allocated may be 2.412 GHz, a center frequency of a 20 MHz channel to which a channel index 2 is allocated may be 2.417 GHz, and a center frequency of a 20 MHz channel to which a channel index N is allocated may be (2.407+0.005*N) GHz. The channel index may be called in various terms such as a channel number or the like. Specific numerical values of the channel index and center frequency may be changed.

FIG. 15 exemplifies 4 channels within a 2.4 GHz band. Each of 1st to 4th frequency domains 1510 to 1540 shown herein may include one channel. For example, the 1st frequency domain 1510 may include a channel 1 (a 20 MHz channel having an index 1). In this case, a center frequency of the channel 1 may be set to 2412 MHz. The 2nd frequency domain 1520 may include a channel 6. In this case, a center frequency of the channel 6 may be set to 2437 MHz. The 3rd frequency domain 1530 may include a channel 11. In this case, a center frequency of the channel 11 may be set to 2462 MHz. The 4th frequency domain 1540 may include a channel 14. In this case, a center frequency of the channel 14 may be set to 2484 MHz.

FIG. 16 illustrates an example of a channel used/supported/defined within a 5 GHz band.

The 5 GHz band may be called in other terms such as a second band or the like. The 5 GHz band may imply a frequency domain in which channels of which a center frequency is greater than or equal to 5 GHz and less than 6 GHz (or less than 5.9 GHz) are used/supported/defined. Alternatively, the 5 GHz band may include a plurality of channels between 4.5 GHz and 5.5 GHz. A specific numerical value shown in FIG. 16 may be changed.

A plurality of channels within the 5 GHz band include an unlicensed national information infrastructure (UNII)-1, a UNII-2, a UNII-3, and an ISM. The INII-1 may be called UNII Low. The UNII-2 may include a frequency domain called UNIT Mid and UNII-2Extended. The UNII-3 may be called UNII-Upper.

A plurality of channels may be configured within the 5 GHz band, and a bandwidth of each channel may be variously set to, for example, 20 MHz, 40 MHz, 80 MHz, 160 MHz, or the like. For example, 5170 MHz to 5330 MHz frequency domains/ranges within the UNII-1 and UNII-2 may be divided into eight 20 MHz channels. The 5170 MHz to 5330 MHz frequency domains/ranges may be divided into four channels through a 40 MHz frequency domain. The 5170 MHz to 5330 MHz frequency domains/ranges may be divided into two channels through an 80 MHz frequency domain. Alternatively, the 5170 MHz to 5330 MHz frequency domains/ranges may be divided into one channel through a 160 MHz frequency domain.

FIG. 17 illustrates an example of a channel used/supported/defined within a 6 GHz band.

The 6 GHz band may be called in other terms such as a third band or the like. The 6 GHz band may imply a frequency domain in which channels of which a center frequency is greater than or equal to 5.9 GHz are used/supported/defined. A specific numerical value shown in FIG. 17 may be changed.

For example, the 20 MHz channel of FIG. 17 may be defined starting from 5.940 GHz. Specifically, among 20 MHz channels of FIG. 17, the leftmost channel may have an index 1 (or a channel index, a channel number, etc.), and 5.945 GHz may be assigned as a center frequency. That is, a center frequency of a channel of an index N may be determined as (5.940+0.005*N) GHz.

Accordingly, an index (or channel number) of the 2 MHz channel of FIG. 17 may be 1, 5, 9, 13, 17, 21, 25, 29, 33, 37, 41, 45, 49, 53, 57, 61, 65, 69, 73, 77, 81, 85, 89, 93, 97, 101, 105, 109, 113, 117, 121, 125, 129, 133, 137, 141, 145, 149, 153, 157, 161, 165, 169, 173, 177, 181, 185, 189, 193, 197, 201, 205, 209, 213, 217, 221, 225, 229, 233. In addition, according to the aforementioned (5.940+0.005*N)GHz rule, an index of the 40 MHz channel of FIG. 17 may be 3, 11, 19, 27, 35, 43, 51, 59, 67, 75, 83, 91, 99, 107, 115, 123, 131, 139, 147, 155, 163, 171, 179, 187, 195, 203, 211, 219, 227.

Although 20, 40, 80, and 160 MHz channels are illustrated in the example of FIG. 17, a 240 MHz channel or a 320 MHz channel may be additionally added.

Hereinafter, a PPDU transmitted/received in a STA of the present specification will be described.

FIG. 18 illustrates an example of a PPDU used in the present specification.

The PPDU 1800 depicted in FIG. 18 may be referred to as various terms such as an EHT PPDU, a TX PPDU, an RX PPDU, a first type or N-th type PPDU, or the like. In addition, the EHT PPDU may be used in an EHT system and/or a new WLAN system enhanced from the EHT system.

The subfields 1801 to 1810 depicted in FIG. 18 may be referred to as various terms. For example, a SIG A field 1805 may be referred to an EHT-SIG-A field, a SIG B field 1806 may be referred to an EHT-SIG-B, a STF field 1807 may be referred to an EHT-STF field, and an LTF field 1808 may be referred to an EHT-LTF.

The subcarrier spacing of the L-LTF, L-STF, L-SIG, and RL-SIG fields 1801, 1802, 1803, and 1804 of FIG. 18 can be set to 312.5 kHz, and the subcarrier spacing of the STF, LTF, and Data fields 1807, 1808, and 1809 of FIG. 18 can be set to 78.125 kHz. That is, the subcarrier index of the L-LTF, L-STF, L-SIG, and RL-SIG fields 1801, 1802, 1803, and 1804 can be expressed in unit of 312.5 kHz, and the subcarrier index of the STF, LTF, and Data fields 1807, 1808, and 1809 can be expressed in unit of 78.125 kHz.

The SIG A and/or SIG B fields of FIG. 18 may include additional fields (e.g., a SIG C field or one control symbol, etc.). The subcarrier spacing of all or part of the SIG A and SIG B fields may be set to 312.5 kHz, and the subcarrier spacing of all or part of newly-defined SIG field(s) may be set to 312.5 kHz. Meanwhile, the subcarrier spacing for a part of the newly-defined SIG field(s) may be set to a pre-defined value (e.g., 312.5 kHz or 78.125 kHz).

In the PPDU of FIG. 18, the L-LTF and the L-STF may be the same as conventional L-LTF and L-STF fields.

The L-SIG field of FIG. 18 may include, for example, bit information of 24 bits. For example, the 24-bit information may include a rate field of 4 bits, a reserved bit of 1 bit, a length field of 12 bits, a parity bit of 1 bit, and a tail bit of 6 bits. For example, the length field of 12 bits may include information related to the number of octets of a corresponding Physical Service Data Unit (PSDU). For example, the length field of 12 bits may be determined based on a type of the PPDU. For example, when the PPDU is a non-HT, HT, VHT PPDU or an EHT PPDU, a value of the length field may be determined as a multiple of 3. For example, when the PPDU is an HE PPDU, the value of the length field may be determined as “a multiple of 3”+1 or “a multiple of 3”+2. In other words, for the non-HT, HT, VHT PPDI or the EHT PPDU, the value of the length field may be determined as a multiple of 3, and for the HE PPDU, the value of the length field may be determined as “a multiple of 3”+1 or “a multiple of 3”+2.

For example, the transmitting STA may apply BCC encoding based on a 1/2 coding rate to the 24-bit information of the L-SIG field. Thereafter, the transmitting STA may obtain a BCC coding bit of 48 bits. BPSK modulation may be applied to the 48-bit coding bit, thereby generating 48 BPSK symbols. The transmitting STA may map the 48 BPSK symbols to positions except for a pilot subcarrier {subcarrier index −21, −7, +7, +21} and a DC subcarrier {subcarrier index 0}. As a result, the 48 BPSK symbols may be mapped to subcarrier indices −26 to −22, −20 to −8, −6 to −1, +1 to +6, +8 to +20, and +22 to +26. The transmitting STA may additionally map a signal of {−1, −1, −1, 1} to a subcarrier index {−28, −27, +27, +28}. The aforementioned signal may be used for channel estimation on a frequency domain corresponding to {−28, −27, +27, +28}.

The transmitting STA may generate an RL-SIG which is identical to the L-SIG. BPSK modulation may be applied to the RL-SIG. The receiving STA may figure out that the RX PPDU is the HE PPDU or the EHT PPDU, based on the presence of the RL-SIG.

After the RL-SIG of FIG. 18, for example, EHT-SIG-A or one control symbol may be inserted. A symbol contiguous to the RL-SIG (i.e., EHT-SIG-A or one control symbol) may include 26 bit information and may further include information for identifying the type of the EHT PPDU. For example, when the EHT PPDU is classified into various types (e.g., an EHT PPDU supporting an SU mode, an EHT PPDU supporting a MU mode, an EHT PPDU related to the Trigger Frame, an EHT PPDU related to an Extended Range transmission, etc.), Information related to the type of the EHT PPDU may be included in a symbol contiguous to the RL-SIG.

A symbol contiguous to the RL-SIG may include, for example, information related to the length of the TXOP and information related to the BSS color ID. For example, the SIG-A field may be contiguous to the symbol contiguous to the RL-SIG (e.g., one control symbol). Alternatively, a symbol contiguous to the RL-SIG may be the SIG-A field.

For example, the SIG-A field may include 1) a DL/UL indicator, 2) a BSS color field which is an identifier of a BSS, 3) a field including information related to the remaining time of a current TXOP duration, 4) a bandwidth field including information related to the bandwidth, 5) a field including information related to an MCS scheme applied to an HE-SIG B, 6) a field including information related to whether a dual subcarrier modulation (DCM) scheme is applied to the HE-SIG B, 7) a field including information related to the number of symbols used for the HE-SIG B, 8) a field including information related to whether the HE-SIG B is generated over the entire band, 9) a field including information related to the type of the LTF/STF, 10) a field indicating the length of the HE-LTF and a CP length.

The SIG-B of FIG. 18 may include the technical features of HE-SIG-B shown in the example of FIGS. 8 to 9 as it is.

An STF of FIG. 18 may be used to improve automatic gain control estimation in a multiple input multiple output (MIMO) environment or an OFDMA environment. An LTF of FIG. 18 may be used to estimate a channel in the MIMO environment or the OFDMA environment.

The EHT-STF of FIG. 18 may be set in various types. For example, a first type of STF (e.g., 1× STF) may be generated based on a first type STF sequence in which a non-zero coefficient is arranged with an interval of 16 subcarriers. An STF signal generated based on the first type STF sequence may have a period of 0.8 μs, and a periodicity signal of 0.8 μs may be repeated 5 times to become a first type STF having a length of 4 μs. For example, a second type of STF (e.g., 2× STF) may be generated based on a second type STF sequence in which a non-zero coefficient is arranged with an interval of 8 subcarriers. An STF signal generated based on the second type STF sequence may have a period of 1.6 μs, and a periodicity signal of 1.6 μs may be repeated 5 times to become a second type STF having a length of 8 μs. For example, a third type of STF (e.g., 4× STF) may be generated based on a third type STF sequence in which a non-zero coefficient is arranged with an interval of 4 subcarriers. An STF signal generated based on the third type STF sequence may have a period of 3.2 μs, and a periodicity signal of 3.2 μs may be repeated 5 times to become a second type STF having a length of 16 μs. Only some of the first to third type EHT-STF sequences may be used. In addition, the EHT-LTF field may also have first, second, and third types (i.e., 1×, 2×, 4× LTF). For example, the first/second/third type LTF field may be generated based on an LTF sequence in which a non-zero coefficient is arranged with an interval of 4/2/1 subcarriers. The first/second/third type LTF may have a time length of 3.2/6.4/12.8 μs. In addition, Guard Intervals (GIs) with various lengths (e.g., 0.8/1/6/3.2 μs) may be applied to the first/second/third type LTF.

Information related to the type of STF and/or LTF (including information related to GI applied to the LTF) may be included in the SIG A field and/or the SIG B field of FIG. 18.

The PPDU of FIG. 18 may support various bandwidths. For example, the PPDU of FIG. 18 may have a bandwidth of 20/40/80/160/240/320 MHz. For example, at least one field (e.g., STF, LTF, data) of FIG. 18 may be configured based on RUs illustrated in FIGS. 5 to 7, and the like. For example, when there is one receiving STA of the PPDU of FIG. 18, all fields of the PPDU of FIG. 18 may occupy the entire bandwidth. For example, when there are multiple receiving STAs of the PPDU of FIG. 18 (i.e., when MU PPDU is used), some fields (e.g., STF, LTF, data) of FIG. 18 may be configured based on the RUs shown in FIGS. 5 to 7. For example, the STF, LTF, and data fields for the first receiving STA of the PPDU may be transmitted/received through a first RU, and the STF, LTF, and data fields for the second receiving STA of the PPDU may be transmitted/received through a second RU. In this case, the locations/positions of the first and second RUs may be determined based on FIGS. 5 to 7, and the like.

The PPDU of FIG. 18 may be determined (or identified) as an EHT PPDU based on the following method.

A receiving STA may determine a type of an RX PPDU as the EHT PPDU, based on the following aspect. For example, the RX PPDU may be determined as the EHT PPDU: 1) when a first symbol after an L-LTF signal of the RX PPDU is a BPSK symbol; 2) when RL-SIG in which the L-SIG of the RX PPDU is repeated is detected; and 3) when a result of applying “module 3” to a value of a length field of the L-SIG of the RX PPDU is detected as “0”. When the RX PPDU is determined as the EHT PPDU, the receiving STA may detect a type of the EHT PPDU (e.g., an SU/MU/Trigger-based/Extended Range type), based on bit information included in a symbol after the RL-SIG of FIG. 18. In other words, the receiving STA may determine the RX PPDU as the EHT PPDU, based on: 1) a first symbol after an L-LTF signal, which is a BPSK symbol; 2) RL-SIG contiguous to the L-SIG field and identical to L-SIG; 3) L-SIG including a length field in which a result of applying “modulo 3” is set to “0”; and 4) a 3-bit PHY version identifier of the aforementioned U-SIG (e.g., a PHY version identifier having a first value).

For example, the receiving STA may determine the type of the RX PPDU as the EHT PPDU, based on the following aspect. For example, the RX PPDU may be determined as the HE PPDU: 1) when a first symbol after an L-LTF signal is a BPSK symbol; 2) when RL-SIG in which the L-SIG is repeated is detected; and 3) when a result of applying “module 3” to a value of a length field of the L-SIG is detected as “1” or “2”.

For example, the receiving STA may determine the type of the RX PPDU as a non-HT, HT, and VHT PPDU, based on the following aspect. For example, the RX PPDU may be determined as the non-HT, HT, and VHT PPDU: 1) when a first symbol after an L-LTF signal is a BPSK symbol; and 2) when RL-SIG in which L-SIG is repeated is not detected. In addition, even if the receiving STA detects that the RL-SIG is repeated, when a result of applying “modulo 3” to the length value of the L-SIG is detected as “0”, the RX PPDU may be determined as the non-HT, HT, and VHT PPDU.

In the following example, a signal represented as a (TX/RX/UL/DL) signal, a (TX/RX/UL/DL) frame, a (TX/RX/UL/DL) packet, a (TX/RX/UL/DL) data unit, (TX/RX/UL/DL) data, or the like may be a signal transmitted/received based on the PPDU of FIG. 18. The PPDU of FIG. 18 may be used to transmit/receive frames of various types. For example, the PPDU of FIG. 18 may be used for a control frame. An example of the control frame may include a request to send (RTS), a clear to send (CTS), a power save-poll (PS-poll), BlockACKReq, BlockAck, a null data packet (NDP) announcement, and a trigger frame. For example, the PPDU of FIG. 18 may be used for a management frame. An example of the management frame may include a beacon frame, a (re-)association request frame, a (re-)association response frame, a probe request frame, and a probe response frame. For example, the PPDU of FIG. 18 may be used for a data frame. For example, the PPDU of FIG. 18 may be used to simultaneously transmit at least two or more of the control frame, the management frame, and the data frame.

FIG. 19 illustrates an example of a modified transmission device and/or receiving device of the present specification.

Each device/STA of the sub-figure (a)/(b) of FIG. 1 may be modified as shown in FIG. 19. A transceiver 630 of FIG. 19 may be identical to the transceivers 113 and 123 of FIG. 1. The transceiver 630 of FIG. 19 may include a receiver and a transmitter.

A processor 610 of FIG. 19 may be identical to the processors 111 and 121 of FIG. 1. Alternatively, the processor 610 of FIG. 19 may be identical to the processing chips 114 and 124 of FIG. 1.

A memory 620 of FIG. 19 may be identical to the memories 112 and 122 of FIG. 1. Alternatively, the memory 620 of FIG. 19 may be a separate external memory different from the memories 112 and 122 of FIG. 1.

Referring to FIG. 19, a power management module 611 manages power for the processor 610 and/or the transceiver 630. A battery 612 supplies power to the power management module 611. A display 613 outputs a result processed by the processor 610. A keypad 614 receives inputs to be used by the processor 610. The keypad 614 may be displayed on the display 613. A SIM card 615 may be an integrated circuit which is used to securely store an international mobile subscriber identity (IMSI) and its related key, which are used to identify and authenticate subscribers on mobile telephony devices such as mobile phones and computers.

Referring to FIG. 19, a speaker 640 may output a result related to a sound processed by the processor 610. A microphone 641 may receive an input related to a sound to be used by the processor 610.

Mesh Wi-Fi (i.e., Multi-AP Solution) is gaining acceptance in the market for better coverage, easier deployment and higher throughput.

It is desirable to improve the performance of the Mesh Wi-Fi by joint optimization of MAC and PHY for multi-AP system. Hardware for multi-AP systems is already on the market and costs little, unlike 16 spatial-stream system.

There are excellent techniques for improving the performance of multi-AP systems. The examples of the techniques include distributed MIMO, coordinated transmission, space/time/frequency sharing and reuse, effective relay scheme, and the like.

FIG. 20 shows an example of activating distributed MIMO transmission (e.g., joint transmission). Referring to FIG. 20, AP1 may start distributed MIMO transmission by sending a coordination signal to an AP2 and an AP3. The AP2 and AP3 may transmit/receive data to and from multiple STAs using OFDMA and MU-MIMO within one data packet. A STA2 and a STA3 may be allocated to different resource units (RUs), and each RU is a frequency segment. A STA1 and a STA4 may be allocated in the same resource unit using MU-MIMO. Each RU may be transmitted in multiple spatial streams.

FIG. 21 is a diagram illustrating multi-AP coordination.

Multi-AP coordination utilizes a wired (e.g., enterprise) or wireless (e.g., home mesh) backbone for data and clock synchronizations.

In addition, the multi-AP coordination has improved link budget and regulatory power limits over single APs with large antenna arrays.

Techniques of the multi-AP coordination include null steering for interference avoidance, joint beamforming, and joint MU-MIMO.

EXAMPLE 1 Null Steering for Interference Avoidance

FIG. 22 shows an example of a null steering operation for interference avoidance. The null steering for interference avoidance may be useful when the multi-AP has a large dimension (e.g., 4×4 or 8×8).

FIG. 23 shows an example in which AP coordination and interference are controlled.

Coordinated scheduling: The coordinated scheduling may mitigate/reduce the number of collisions from APs/STAs of other BSSs.

In addition, the coordinated scheduling is a distributed mechanism and increases the number/probability of parallel transmission in a coordinated manner than spatial reuse.

-   Message exchange between APs may be required.

FIG. 24 shows interference nulling and distributed joint beamforming.

Coordinated beamforming: In the coordinated beamforming, downlink transmission can be performed simultaneously without co-channel interference due to beamforming, such as designating a nulling point to another STA or using distributed joint beamforming.

In addition, the coordinated beamforming may be suitable for managed deployments (e.g., corporate offices, hotels) and has the advantages of area throughput and consistent user experience. In addition, the coordinated beamforming may require coordinated downlink scheduling and improved MU sounding to reduce overhead, synchronization, and the like.

FIG. 25 shows an example of coordinated beamforming.

A solid arrow in FIG. 25 indicates data transmission within a BSS STA, and a dotted arrow in FIG. 25 is a null transmitted to the OBSS STAs. According to a main attribute of the coordinated beamforming, a signal for a user may be transmitted from only one AP which forms a null to the OBSS STA.

FIG. 26 is a diagram for explaining C-OFDMA.

The coordinated-OFDMA (C-OFDMA) extends 11ax OFDMA which was based on a single BSS scenario to a multiple BSS scenario. In addition, the C-OFDMA may efficiently utilize frequency resources throughout the network. In addition, the C-OFDMA may improve efficiency when BSS traffic is not fully utilizing resources.

Referring to FIG. 26, a spectrum 2610 used for 20 MHz transmission of BSS1 and a spectrum 2620 used for 20 MHz transmission of BSS2 exist in a total band of 40 MHz. Synchronized transmission may be performed to obtain orthogonality. The STA1, STA2 and STA3 are allocated to the spectrum 2610 used for transmission of BSS1, and the STA4 and STAS are allocated to spectrum 2620 used for transmission of BSS2.

FIG. 27 shows an example of joint transmission (e.g., distributed MIMO).

The joint transmission (J-Tx or JTX) may mean performing joint beamforming to a single STA. Referring to FIG. 27, one STA is being serviced by AP1 and AP2.

The joint transmission may have more stringent synchronization requirements and should be looked at separately. The joint transmission may be performed more easily than joint processing transmission for multiple STAs. However, the joint transmission may exploit beamforming and power gain from multiple APs.

FIG. 28 shows an example of performing joint transmission through the M-AP and the S-AP.

A master AP (M-AP) may act as an AP coordinator. A slave AP (S-AP) may participate in joint transmission coordinated by the M-AP, and may have both the functions of a STA and an AP. Referring to FIG. 28, S-AP1 and S-AP2 have a STA function in a coordination step and an AP function in a joint transmission step.

Multi-AP coordination technology in the wireless LAN system minimizes interference between BSSs during data transmission or increases data transmission efficiency by participating in two or more APs on a specific time point of data transmission/reception to a terminal by sharing channel feedback information and scheduling information of the terminal between APs when transmitting and receiving data frames between the terminal and the APs. In the wireless LAN system, this Multi-AP coordination technology has not been standardized yet, but recently, in the IEEE802.11 EHT TIG, standardization related to the Multi-AP coordination as a next-generation technology is being newly discussed. In the present specification, a method in which multiple APs can participate in data transmission using the multi-AP coordination in a wireless LAN system is proposed.

FIG. 29 shows an example of a network configured with multiple APs.

Referring to FIG. 29, a master AP (M-AP) may select a plurality of APs performing multi-AP communication by performing a selection procedure for multi-AP coordination with slave APs (S-APs). The M-AP and S-AP described in FIG. 29 may be configured, for example, based on the STA of FIG. 1. S-AP1 to S-AP3 selected by the M-AP may perform data transmission (e.g., joint transmission or distributed MIMO) to the STA by performing a sounding procedure. Descriptions of the M-AP, S-AP(s), and STA shown in FIG. 29 are as follows.

<1> Master AP

A master AP may initiate and control Joint Transmission (JTX).

The master AP may group the slave-APs and manage links with the slave-APs to share information between the slave-APs.

The master AP may manage the information of the BSS configured by the slave APs and the information of the STAs that have established an association within the corresponding BSS.

<2> Slave-AP

A slave-AP may establish an association with the master AP. The slave-AP may share control information, management information, data traffic, and the like with the master AP.

The slave-AP may perform the same function as the AP that can form the BSS in the existing WLAN.

<3> STA

As in the existing WLAN, the STA may establish an association with the slave AP or the master AP to configure a BSS.

The master AP and slave AP may directly transmit and receive each other.

The master AP and the STA may not be able to directly transmit and receive each other.

The slave AP (associated with STA) and the STA may directly transmit and receive each other.

One of the slave APs may become (or operate/serve as) a master AP.

FIG. 30 is a diagram illustrating an example of a method in which a plurality of APs perform joint transmission to a plurality of STAs.

The communication network of FIG. 30 may be the same as the network of FIG. 29. Referring to FIG. 30, the joint transmission procedure may consist of Step 1 to Step 7. The frame described in FIG. 30 may be configured, for example, based on the PPDU of FIG. 18. The transmitting apparatus described in FIG. 30 may be configured, for example, based on the STA of FIG. 1.

Step 1: The master AP can transmit a JTX trigger frame to a slave-AP1, a slave-AP2, and a slave-AP3.

<Transmission Method>

The JTX trigger frame can be transmitted to multiple slave APs at once.

The master AP may transmit the JTX trigger frame only to specific slave APs or to all slave APs that can receive the JTX trigger frame transmitted by the master AP.

<Content or Information>

The address of the STA that receives the JTX, BSS information to which the STA belongs, and an address of the slave AP that has established an association with the STA may be included.

<Operation>

The slave APs that have received the JTX trigger frame may perform an operation to synchronize (e.g., timing, carrier frequency offset (CFO), sampling frequency offset (SFO), phase drift) with the master AP or slave APs. That is, the JTX trigger frame may have the effect of providing the S-AP with information necessary to perform CFO compensation, SFO compensation, phase correction, synchronization, and the like.

A slave-AP1 may prepare to transmit a Null Data Packet (NDP) request frame to an associated STA-a.

A slave-AP2 may prepare to transmit a Null Data Packet (NDP) request frame to an associated ‘STA-b’.

A slave-AP3, which is not associated with the STAs (e.g., the STA-a, STA-b), may prepare to receive the NDP frame to be sent by the corresponding STAs (e.g., the STA-a, STA-b).

Step 2: The slave APs (associated with STAs) may transmit a JTX NDP request frame to their associated STAs. Step 2-a: For example, the slave-AP1 may transmit a JTX NDP request frame to the ‘STA-a’. Step 2-b: The slave-AP2 may transmit a JTX NDP request frame to the ‘STA-b’.

<Transmission Method>

For example, slave APs (associated with STAs) may transmit the same JTX NDP request frame to their associated STAs. For example, slave APs (associated with STAs) may transmit different JTX NDP request frames including information specific to each STA to their associated STAs.

<Content or Information>

When a slave AP (associated with STA) transmits the same JTX NDP request frame to its associated STAs, the JTX NDP request frame may include addresses of all STAs receiving the JTX NDP request frame, or addresses (or indicators) of the slave APs that will receive a JTX NDP frame in the future.

When a slave AP (associated with STA) transmits different JTX NDP request frames including information specific to each STA to its associated STAs, the JTX NDP request frame may include an address of one STA receiving the JTX NDP request frame, and/or addresses (or indicators) of the slave APs that will receive a JTX NDP frames in the future.

<Operation>

The STA that has received the JTX NDP request frame may prepare to transmit the JTX NDP frame.

Step 2-1: If the STA can directly receive the frame transmitted by the master AP, the procedure in Step 2 may be omitted, and the master AP may directly transmit the JTX NDP request frame to the STA. Also, the master AP may perform steps 1) and 2) at once. For example, the master AP may transmit the contents of the JTX trigger frame and the JTX NDP request to the slave APs at once. When the STAs receive the contents of the JTX trigger frame and the JTX NDP request at once, the STAs can perform both the operations of Step 1 and Step 2.

Step 3: The STA transmits JTX NDP frame to slave APs. Step 3-a: For example, the ‘STA-a’ may transmit a JTX NDP frame to the slave APs (e.g., the slave-AP1, slave-AP2, and slave-AP3). Step 3-b: For example, the ‘STA-b’ may transmit a JTX NDP frame to the slave APs (e.g., the slave-AP1, slave-AP2, and slave-AP3).

<Transmission Method>

The STA may transmit only a preamble without a payload like a conventional NDP format, or may transmit a frame including the payload.

When transmitting the JTX NDP frame, the STA may set the number of LTFs in the PPDU to be less than or equal to the number of supportable spatial streams.

<Content or Information>

When the JTX NDP frame includes only a preamble without a payload, the content may be included in the PHY header.

When the JTX NDP frame includes the payload, the relevant content may be included in the payload and/or the PHY header.

The JTX NDP frame may, individually or by grouping, include addresses or indicators of slave APs

<Operation>

The slave APs that have received the JTX NDP frame may estimate a channel with the STA that transmitted the JTX NDP frame.

The slave APs that have received the JTX NDP frame may obtain channel information (e.g., Received Signal Strength Indicator (RSSI), signal-to-noise ratio (SNR), signal-to-interference-plus ratio (SINR)) with regard to the STA that transmitted the JTX NDP frame. That is, the JTX NDP frame may have the effect of causing the slave AP to estimate the channel between the slave AP and the STA.

The slave APs that have received the JTX NDP frames may perform an operation to synchronize (e.g., timing, CFO, SFO, Phase drift synchronize) the STAs with the slave APs. That is, the JTX NDP frame may have the effect of providing information related to the synchronization with the slave AP.

The operation of Step 3 describes a channel estimation method in multi-user (MU) transmission using channel reciprocity. The channel reciprocity refers to a method of estimating a downlink (DL) channel through a sounding procedure of an uplink (UL) channel. Therefore, even if the slave AP does not directly transmit a reference signal, it can have the effect of estimating a channel through the reference signal (e.g., JTX NDP frame) transmitted by the STA.

Step 3-1: If the channel reciprocity is not supported, the STA may transmit a newly defined JTX NDP frame including only the LTF for one stream without using the existing NDP frame. In this case, the STA may report only the power strength, and does not support Multi-Input Multi-Output (MIMO) when transmitting the JTX NDP frame. Also at this time, the newly defined frame includes the indicator of the slave APs in order to check whether the frame is intended to the slave APs.

Step 4: The master AP can transmit a JTX NDP feedback trigger frame to slave APs. The JTX NDP feedback trigger frame is a frame for requesting or triggering the JTX NDP feedback frame.

<Transmission Method>

The master AP may transmit a JTX NDP feedback trigger frame to slave APs (e.g., slave-AP1, slave-AP2, and slave-AP3) at once.

<Content or Information>

The indicator (e.g., an ID or a group ID of the slave AP) or an address of the slave AP that is the same as the indicator of the slave APs included in the JTX trigger frame may be included in the JTX NDP feedback trigger frame.

<Operation>

The slave APs that have received the JTX NDP feedback trigger frame may synchronize (e.g., Timing, CFO, SFO, Phase drift synchronization) with the master AP or slave APs, and prepare to transmit the JTX NDP feedback frame. The JTX NDP feedback trigger frame may also have the effect of providing information related to the operation of synchronizing to the slave AP.

Step 5: The slave APs may transmit a JTX NDP feedback frame to the master AP.

<Transmission Method>

The slave APs may transmit a JTX NDP feedback frame in a UL MU-MIMO or UL MU-OFDMA scheme.

Alternatively, each slave AP may sequentially transmit the JTX NDP feedback frame.

<Content or Information>

The JTX NDP feedback frame may include a channel estimation value between the slave AP transmitting the JTX NDP feedback frame and each STA.

<Operation>

The master AP which has received the JTX NDP feedback frame may select slave APs to perform JTX based on the JTX NDP feedback frame. For example, the master AP which has received the JTX NDP feedback frame may integrate individual channel estimation values between the slave APs and STAs into one channel, and select the most suitable slave APs for the JTX based on the integrated channel information. That is, the JTX NDP feedback frame may have the effect of providing the M-AP with information for selecting the most suitable slave AP for the JTX.

Step 6: The master AP can transmit a JTX selection frame to the selected slave APs based on the JTX NDP feedback.

<Transmission Method>

The master AP can transmit the JTX selection frame only to the slave APs that will finally participate in the JTX among the slave APs included in the JTX trigger frame and the JTX NDP feedback trigger frame. The master AP can share data with the slave APs along with the JTX selection frame transmission. For example, the master AP may transmit data to be transmitted in the JTX together with the JTX selection frame.

<Content or Information>

The JTX selection frame may include information relate to JTX settings such as antenna information to be used for each slave AP, the number of streams, Modulation and Coding Scheme (MCS), and PSDU length. Since the master AP notifies the slave AP of JTX-related configuration information through the JTX selection frame, the slave AP can have the effect of minimizing the operation for transmission.

Alternatively, the JTX selection frame may include only channel information, selection information, and information supporting a procedure for synchronization. A slave AP may directly perform configuration for the JTX transmission.

The JTX selection frame may include addresses or indicators of the slave APs participating in the JTX.

The JTX selection frame may contain data to be transmitted in the JTX. Depending on the purpose, the master AP may share the same data or different data to each slave AP.

<Operation>

The selected slave APs that have received the JTX selection frame can prepare to start the JTX.

Step 6-1: The master AP performs a channel estimation procedure for the JTX by sending a JTX NDP request once again before sharing data with the slave APs, and can finally select slave APs to participate in the JTX.

Step 6-2: If the channel reciprocity is not supported, channel estimation for the JTX may be performed using the JTX NDP frame transmitted to the STA by the slave APs selected through the selection procedure. That is, since the channel reciprocity is not supported, the selected slave APs can directly transmit the JTX NDP frame through DL to perform channel estimation.

Step 7: The selected slave APs may transmit data to STAs (e.g., STA-a, STA-b) using JTX. For example, the STAs that receive the JTX transmission may be STAs whose addresses are included in the JTX trigger frame.

The JTX trigger frame, JTX NDP request frame, JTX NDP frame, JTX NDP feedback trigger frame, JTX NDP feedback frame, and JTX selection frame described in FIG. 30 may be referred to as various names. The joint transmission (JTX) is also not limited to the name JTX, and may refer to a method in which a plurality of APs cooperate to transmit a signal to an STA. In addition, the master AP and the slave AP may also be referred to as different names.

In FIG. 30, a case in which STAs are associated with other slave APs has been described as an example. However, the procedure of FIG. 30 may be applied even in a situation in which all STAs (e.g., STA-a, STA-b) are associated with one slave AP (e.g., slave-AP1). In this case, the operation and procedure performed in the link between the slave-AP2 and the STA-b in Step 2-b may be performed by replacing the slave-AP2 with the slave-AP1. For example, in Step 2, the slave-AP1 may transmit a JTX NDP request frame to the STA-a and the STA-b.

FIG. 31 shows an example of a network configured with multiple APs.

Referring to FIG. 31, a master AP (M-AP) may select a plurality of APs performing multi-AP communication by performing a selection procedure for multi-AP coordination with slave-APs (S-APs). The M-AP and S-AP described in FIG. 31 may be configured, for example, based on the STA of FIG. 1. The S-AP1 to S-AP3 selected by the M-AP may perform data transmission (e.g., joint transmission or distributed MIMO) to the STA by performing a sounding procedure. Descriptions of the M-AP, S-AP(s) and STA shown in FIG. 31 are as follows.

<1> Master AP

The master AP may initiate and control Joint Transmission (JTX).

The master AP may group the slave-APs and manage links with the slave-APs to share information between the slave-APs.

The master AP may manage the information of the BSS configured by the slave APs and the information of the STAs that have established an association with the corresponding BSS.

<2> Slave-AP

The slave-AP may an establish association with the master AP. The slave-AP may share control information, management information, data traffic, and the like with the master AP.

The Slave-AP may perform the same function as the AP that can form the BSS in the existing WLAN.

<3> STA

The master AP and slave AP may directly transmit and receive each other.

The master AP and the STA may not be able to directly transmit and receive each other.

The slave AP (associated with the STA) and the STA can directly transmit and receive each other.

One of the slave APs can become (or operate as) a master AP.

FIG. 32 is a diagram illustrating an example of a method for a plurality of APs to perform multi-AP transmission (MAP) to an STA.

An example of FIG. 32 is an embodiment in which the master AP cannot directly transmit/receive with the STA.

The communication network of FIG. 32 may be the same as the network of FIG. 31. Referring to FIG. 32, the Multi-AP transmission procedure may consist of Step 1 to Step 6. The frame described in FIG. 32 may be configured, for example, based on the PPDU of FIG. 18. The transmitting apparatus described in FIG. 32 may be configured, for example, based on the STA of FIG. 1.

Step 1: The master AP may transmit a MAP trigger frame to a slave-AP1, a slave-AP2, and a slave-AP3.

<Transmission Method>

The MAP trigger frame can be transmitted to multiple slave APs at once.

The master AP may transmit a MAP trigger frame only to specific slave APs, or the master AP may transmit a MAP trigger PPDU including a broadcast address (e.g., PPDU including the MAP trigger frame) to all slave APs which may receive signals from the master AP.

<Content or Information>

The MAP trigger frame may include an address of the STA that receives the MAP transmission, BSS information to which the STA belongs, an address of the slave AP that has established an association with the STA, and addresses or broadcast addresses of the slave APs that receive the MAP trigger frame.

<Operation>

The slave APs that have received the MAP trigger frame may perform an operation to synchronize (timing, carrier frequency offset (CFO), sampling frequency offset (SFO), and phase drift) with the master AP or slave APs. That is, the MAP trigger frame may have the effect of providing the slave AP with information necessary to perform CFO compensation, SFO compensation, phase correction, synchronization, and the like.

Slave-AP1 being associated with the STA may prepare to transmit a MAP reference request frame.

Slave-AP2 and Slave-AP3 being un-associated with the STA may prepare to receive the MAP reference request frame to be sent by the STA.

Step 2: A slave AP (associated with the STA) may transmit a MAP reference request frame to its associated STA. For example, the slave-AP1 may transmit a MAP reference request frame to the STA.

<Transmission Method>

For example, the master AP may designate a slave AP to transmit the MAP reference request frame through the MAP trigger frame. For example, the master AP may designate a slave AP associated with the STA among the slave APs as a slave AP to transmit the MAP reference request frame. For example, the master AP may designate the slave-AP1 as a slave AP to transmit the MAP reference request frame to the STA.

<Content or Information>

The MAP reference request frame may include an address of the STA that receives the MAP reference request frame, an address of the slave AP that transmits the MAP reference request frame, and/or addresses or indicators of the slave APs that will receive the MAP reference frame in the future.

<Operation>

The STA that has received the MAP reference request frame may prepare to transmit the MAP reference frame.

Step 2-1: If the STA can directly receive the frame transmitted by the master AP (e.g., FIG. 33), the procedure in Step 2 can be omitted, and the master AP may directly send the MAP reference request frame to the STA. Also, the master AP may perform Step 1 and Step 2 at once. For example, the master AP may transmit the contents of the MAP trigger frame and the MAP reference request frame to the slave APs at once. For example, the STA may receive a MAP reference request frame from the master AP. For example, the procedure of Step 2 may be performed simultaneously by integrating the procedure of Step 1 with content and operation.

Step 3: The STA may transmit a MAP reference frame to the slave APs. Step 3-a: For example, the STA may transmit a MAP reference frame to slave APs (e.g., slave-AP1, slave-AP2, and slave-AP3).

<Transmission Method>

The MAP reference frame may include only a preamble without a payload like a conventional null data packet (NDP) format, or may include the payload.

<Content or Information>

When the MAP reference frame includes only the preamble without the payload, the content may be included in the PHY header.

When the MAP reference frame includes the payload, the content may be included in the payload and/or the PHY header.

The MAP reference frame may, individually or by grouping, include addresses or indicators of slave APs.

<Operation>

The slave APs that have received the MAP reference frame may estimate a channel with the STA that transmitted the MAP reference frame. Due to channel reciprocity, the slave AP may have an effect of estimating the channel through the reference signal (e.g., MAP reference frame) transmitted by the STA, even if the slave AP does not directly transmit the reference signal.

The slave APs that have received the MAP reference frames may perform an operation to synchronize the STAs with the slave APs (e.g., Timing, CFO, SFO, Phase drift synchronization). That is, the MAP reference frame may have the effect of providing information related to the operation of synchronizing to the slave AP.

Step 4: The master AP may transmit a MAP feedback request frame to the slave APs.

<Transmission Method>

The master AP may transmit a MAP feedback request frame to slave APs (e.g., the slave-AP1, slave-AP2, and slave-AP3) at once. That is, the master AP may transmit a MAP feedback request frame to the slave-AP1, slave-AP2, and slave-AP3.

<Content or Information>

An address of the receiving STA, BSS information to which the STA belongs, an address of the slave AP that has established an association with the STA, and addresses (individual/group) or indicators (individual/group) of the slave APs that receive the MAP feedback request frame may be included.

<Operation>

The slave APs that have received the MAP NDP feedback request frame may synchronize (e.g., Timing, CFO, SFO, Phase drift) with the master AP or slave APs, and may prepare to transmit the MAP feedback frame. That is, the MAP NDP feedback request frame may have the effect of providing information related to the operation of synchronizing to the slave AP.

Step 5: The slave APs (e.g., the slave-AP1, slave-AP2, and slave-AP3) may transmit a MAP feedback frame to the master AP.

<Transmission Method>

The slave APs may transmit a MAP feedback frame in a UL MU-MIMO or UL MU-OFDMA scheme.

Alternatively, the MAP feedback frame may be transmitted sequentially by one slave AP.

<Content or Information>

The MAP feedback frame may include channel information (e.g., received signal strength indicator (RSSI), signal to noise ratio (SNR), signal to interference noise ratio (SINR), etc.) between the slave AP that transmits the MAP feedback frame and each STA.

<Operation>

The master AP which has received the MAP feedback frame may select slave APs to perform MAP based on the MAP feedback frame. For example, the master AP which has received the MAP NDP feedback frame may integrate individual channel estimation values between the slave APs and the STAs into one channel, and select the most suitable slave APs for the MAP based on the integrated channel information.

Step 6: The master AP may transmit a MAP selection frame to selected slave APs based on MAP NDP feedback.

<Transmission Method>

The master AP may transmit the MAP selection frame only to the slave APs that will finally participate in Multi-AP transmission among the slave APs.

The master AP may share data with the slave APs along with MAP selection frame transmission. For example, the master AP may transmit data to be transmitted based on the MAP together with a MAP selection frame to the slave AP.

<Content or Information>

The MAP selection frame may include information related to the multi-AP transmission, such as RU/channel information, antenna information, number of streams, and MCS (Modulation and Coding Scheme) to be used for each slave AP.

The MAP selection frame may include addresses (individual/group) or indicators (individual/group) of the slave APs participating in the Multi-AP transmission.

The MAP selection frame may include data to be transmitted based on the Multi-AP transmission. Depending on the purpose, the master AP may share the same data or different data to each slave AP.

<Operation>

The selected slave APs that have received the MAP selection frame may prepare to start the Multi-AP transmission.

The slave APs that have received the MAP selection frame may perform an operation to synchronize (e.g., Timing, CFO, SFO, Phase drift) with the master AP or slave APs.

After completing the Multi-AP Selection procedure, a new procedure for Multi-AP transmission may be performed. For example, the master AP may perform a channel estimation procedure for the multi-AP transmission by transmitting a MAP reference request once again before data sharing with the slave APs, and finally select slave APs to participate in MAP.

The MAP trigger frame, MAP reference request frame, MAP reference frame, MAP feedback request frame, MAP feedback frame, and MAP selection frame described in FIG. 32 may be referred to as different names/terminologies. Also, the Multi-AP transmission (MAP) is not limited to the name MAP, and may refer to a method in which a plurality of APs cooperate to transmit a signal to an STA. In addition, the master AP and the slave AP may also be referred to by different names/terminologies.

FIG. 33 is a diagram illustrating an example of a method for a plurality of APs to perform multi-AP transmission to an STA.

An example of FIG. 33 is an embodiment in which the master AP can directly transmit/receive with the STA.

The communication network of FIG. 33 may be the same as the network of FIG. 31. Referring to FIG. 33, the Multi-AP transmission procedure may consist of Step 1 to Step 6, similar to FIG. 32. The frame described in FIG. 33 may be configured, for example, based on the PPDU of FIG. 18. The transmitting apparatus described in FIG. 33 may be configured, for example, based on the STA of FIG. 1.

Step 1: The master AP may transmit a MAP trigger frame to the slave APs (e.g., the slave-AP1, slave-AP2).

Step 2: The master AP may transmit a MAP reference request frame to its associated STA.

Step 3: The STA may transmit a MAP reference frame to the slave APs and the master AP.

Step 4: The master AP may transmit a MAP feedback request frame to the slave APs.

Step 5: The slave APs may transmit a MAP feedback frame to the master AP.

Step 6: The master AP may transmit a MAP Selection frame to the slave AP (e.g., the slave-AP1).

Technical features of FIG. 33 are the same as FIG. 32 except that one of the slave APs (e.g., an AP associated with the STA) operates/serves as the master AP. Accordingly, Step 1 to Step 6 of FIG. 33 may be the same as Step 1 to Step 6 of FIG. 32 except that one of the slave APs operates/serves as the master AP. In FIG. 32, the master AP transmits a MAP reference request frame to the STA through the slave AP, or receives a MAP reference frame from the STA through the slave AP. However, in FIG. 33, the master AP directly transmits/receives a frame to/from the STA.

Hereinafter, the above-described embodiment will be described with reference to FIGS. 18 to 33.

FIG. 34 is a flowchart illustrating a procedure for performing multi-AP transmission in the S-AP based on the present embodiment.

The example of FIG. 34 may be performed in a network environment in which a next-generation wireless LAN system is supported. The next-generation wireless LAN system is a wireless LAN system (e.g., EHT or 802.11be) improved from the 802.11ax system, and may support backward compatibility with the 802.11ax system.

This embodiment may be performed in the S-AP. The S-AP of this embodiment is an STA supporting an Extremely High Throughput (EHT) WLAN system.

The S-AP (i.e., the slave AP) may receive a trigger frame from the M-AP (i.e., the master AP) in S3410. The trigger frame may be transmitted to multiple S-APs at once. The M-AP may transmit the trigger frame only to specific S-APs, or may transmit the trigger frame to all S-APs that can receive the trigger frame transmitted by the M-AP.

The trigger frame may include an address of the STA that receives the multi-AP transmission (e.g., joint transmission), BSS information to which the STA belongs, and an address of the slave AP that has established an association with the STA.

Upon receiving the trigger frame, the S-APs may perform an operation of matching the synchronization (Timing, carrier frequency offset (CFO), sampling frequency offset (SFO), phase drift) with the M-AP or the S-APs.

The S-AP associated with STA(s) may transmit an NDP request frame to its associated STA(s) (S3420). For example, the S-AP associated with the STA may transmit the same NDP request frame to its associated STAs. For example, the S-AP associated with STA(s) may transmit different NDP request frames including information specific to each STA to its associated STAs.

When the S-AP associated with STA(s) transmits the same NDP request frame to its associated STAs, the NDP request frame includes addresses of all STAs that receive the NDP request frame, and/or addresses (or indicators) of the S-APs which will receive an NDP frame in the future.

When the S-AP associated with STA(s) transmits different NDP request frames including information specific to each STA to its associated STAs, each NDP request frame may include an address of one STA which receives the NDP request frame, and/or addresses (or indicators) of the S-APs that will receive the NDP frame in the future.

The STA may transmit the NDP frame to the S-AP (S3430). The STA may transmit only a preamble without a payload like a conventional NDP format, or may transmit a frame including the payload. When transmitting the NDP frame, the STA may set the number of LTFs in the PPDU to be less than or equal to the number of supportable spatial streams.

When the NDP frame includes only the preamble without the payload, the content may be included in the PHY header. When the NDP frame includes the payload, the content may be included in the payload and/or the PHY header. The NDP frame may, individually or by grouping, include addresses or indicators of S-APs.

The S-APs that have received the NDP frame may estimate a channel with the STA that transmitted the NDP frame. The S-APs that have received the NDP frame may obtain channel information (e.g., Received Signal Strength Indicator (RSSI), signal-to-noise ratio (SNR), signal-to-interference-plus-noise ratio (SINR), etc.) with regard to the STA that has transmitted the NDP frame. The S-APs that have received the NDP frames may perform an operation of synchronizing (e.g., Timing, CFO, SFO, Phase drift) with the STAs and the S-APs.

The above operation describes a channel estimation method in multi-user (MU) transmission using channel reciprocity. The channel reciprocity refers to a method of estimating a downlink (DL) channel through a sounding procedure of an uplink (UL) channel.

If the channel reciprocity is not supported, the STA may transmit a new NDP frame including only the LTF for one stream without using the conventional NDP frame. In this case, the STA may report only the power strength, and may not support Multi-Input Multi-Output (MIMO) when transmitting the NDP frame. Likewise in the case, by including an indicator of the S-APs in the newly defined frame, the S-APs can check whether the received frames are intended ones.

The S-AP may receive a feedback request frame from the M-AP (S3440). The feedback request frame is a frame for requesting or triggering an NDP feedback frame. The M-AP may transmit the feedback request frame to the S-APs at once.

The feedback request frame may include an indicator (e.g., an ID or a group ID of the S-AP) or an address of the S-AP whose indicator is same as the indicator of the S-AP included in the trigger frame.

The S-APs may transmit an NDP feedback frame to the M-AP (S3450). The S-AP may transmit the NDP feedback frame in a UL MU-MIMO or UL MU-OFDMA scheme. Alternatively, the NDP feedback frame may be transmitted sequentially by one S-AP.

The NDP feedback frame may include a channel estimation value between the S-AP transmitting the NDP feedback frame and each STA.

Upon receiving the NDP feedback frame, the M-AP may select S-APs to perform multi-AP transmission (e.g., joint transmission) based on the NDP feedback frame. For example, the M-AP receiving the NDP feedback frame may integrate individual channel estimation values between the S-APs and the STA into one channel, and select the most suitable S-AP for the multi-AP transmission based on the integrated channel information.

FIG. 35 is a flowchart illustrating a procedure for performing Multi-AP transmission in an STA according to the present embodiment.

The example of FIG. 35 may be performed in a network environment in which a next-generation wireless LAN system is supported. The next-generation wireless LAN system is a wireless LAN system (e.g., EHT or 802.11be) improved from the 802.11ax system, and may support backward compatibility with the 802.11ax system.

This embodiment may be performed in an STA. The receiving STA of this embodiment may be an STA supporting the Extremely High Throughput (EHT) wireless LAN system.

The STA may receive a NDP request frame (S3510). For example, the STA may receive an NDP request frame from its associated S-AP. For example, an S-AP associated with STA(s) may transmit the same NDP request frame to its associated STAs. For example, the S-AP associated with STA(s) may transmit different NDP request frames including information specific to each STA to its associated STAs.

When the S-AP associated with STA(s) transmits the same NDP request frame to its associated STAs, the NDP request frame includes addresses of all STAs that receive the NDP request frame, and/or addresses (or indicators) of the S-APs that will receive the NDP frame in the future.

When the S-AP associated with STA(s) transmits different NDP request frames including information specific to each STA to its associated STAs, the NDP request frame includes an address of one STA that receive the NDP request frame, and/or addresses (or indicators) of the S-APs that will receive the NDP frame in the future.

The STA may transmit an NDP frame to the S-AP (S3520). The STA may transmit only a preamble without a payload like the conventional NDP format, or may transmit a frame including the payload. When transmitting the NDP frame, the STA may set the number of LTFs in the PPDU to be less than or equal to the number of supportable spatial streams.

When the NDP frame includes only a preamble without a payload, the content may be included in the PHY header. When the NDP frame includes the payload, the content may be included in the payload and/or the PHY header. The NDP frame may, individually or by grouping, include addresses or indicators of S-APs.

The S-APs that have received the NDP frame may estimate a channel with the STA that has transmitted the NDP frame. The S-APs that have received the NDP frame may obtain channel information (Received Signal Strength Indicator (RSSI), signal-to-noise ratio (SNR), and signal-to-interference-plus-noise ratio (SINR), etc.) with regard to the STA that has transmitted the NDP frame. The S-APs that have received the NDP frames may perform an operation of synchronizing (e.g., Timing, CFO, SFO, Phase drift) with the STAs and the S-APs.

The above operation describes a channel estimation method in multi-user (MU) transmission using channel reciprocity. The channel reciprocity refers to a method of estimating a downlink (DL) channel through a sounding procedure of an uplink (UL) channel.

If the channel reciprocity is not supported, the STA may transmit a new NDP frame including only the LTF for one stream without using the conventional NDP frame. In this case, the STA may report only the power strength, and may not support Multi-Input Multi-Output (MIMO) when transmitting the NDP frame. Likewise in the case, by including an indicator of the S-APs in the newly defined frame, the S-APs can check whether the received frames are intended ones.

The STA may receive data from the S-APs (S3530). For example, the selected S-APs may transmit data to the STA using Multi-AP transmission. For example, the STAs receiving the Multi-AP transmission may be STAs whose addresses are included in the trigger frame (e.g., the trigger frame of FIG. 30, FIG. 32, or FIG. 33).

The technical features of the present specification described above may be applied to various devices and methods. For example, the above-described technical features of the present specification may be performed/supported through the apparatus of FIGS. 1 and/or 19. For example, the technical features of the present specification described above may be applied only to a part of FIGS. 1 and/or 19. For example, the technical features of the present specification described above are implemented based on the processing chips 114 and 124 of FIG. 1, or implemented based on the processors 111 and 121 and the memories 112 and 122 of FIG. 1, or may be implemented based on the processor 610 and the memory 620 of FIG. 19. For example, an apparatus herein may include a memory and a processor operatively coupled to the memory, wherein the processor obtains a trigger frame received from a second type AP, and generating a Null Data Packet (NDP) request frame to be transmitted to a station (STA), obtaining a first NDP frame received from the first STA, and obtaining a second NDP frame received from a second STA, obtaining a feedback request frame received from the second type AP, and generating an NDP feedback frame to be transmitted to the second type AP based on the first and second NDP frames.

The technical features of the present specification may be implemented based on a computer readable medium (CRM). For example, the CRM proposed by the present specification can be read by at least one computer including an instruction based on being executed by at least one processor of a first type access point (AP). The computer readable medium may store instructions to perform: receiving a trigger frame from a second type AP; transmitting a Null Data Packet (NDP) request frame to a first station (STA); receiving a first NDP frame from the first STA, and receiving a second NDP frame from a second STA; receiving a feedback request frame from the second type AP; and based on the first and second NDP frames transmitting an NDP feedback frame to the second type AP. The instructions stored in the CRM of the present specification may be executed by at least one processor. At least one processor related to CRM in the present specification may be the processors 111 and 121 or the processing chips 114 and 124 of FIG. 1, or the processor 610 of FIG. 19. Meanwhile, the CRM of the present specification may be the memories 112 and 122 of FIG. 1, the memory 620 of FIG. 19, or a separate external memory/storage medium/disk.

The foregoing technical features of this specification are applicable to various applications or business models. For example, the foregoing technical features may be applied for wireless communication of a device supporting artificial intelligence (AI).

Artificial intelligence refers to a field of study on artificial intelligence or methodologies for creating artificial intelligence, and machine learning refers to a field of study on methodologies for defining and solving various issues in the area of artificial intelligence. Machine learning is also defined as an algorithm for improving the performance of an operation through steady experiences of the operation.

An artificial neural network (ANN) is a model used in machine learning and may refer to an overall problem-solving model that includes artificial neurons (nodes) forming a network by combining synapses. The artificial neural network may be defined by a pattern of connection between neurons of different layers, a learning process of updating a model parameter, and an activation function generating an output value.

The artificial neural network may include an input layer, an output layer, and optionally one or more hidden layers. Each layer includes one or more neurons, and the artificial neural network may include synapses that connect neurons. In the artificial neural network, each neuron may output a function value of an activation function of input signals input through a synapse, weights, and deviations.

A model parameter refers to a parameter determined through learning and includes a weight of synapse connection and a deviation of a neuron. A hyper-parameter refers to a parameter to be set before learning in a machine learning algorithm and includes a learning rate, the number of iterations, a mini-batch size, and an initialization function.

Learning an artificial neural network may be intended to determine a model parameter for minimizing a loss function. The loss function may be used as an index for determining an optimal model parameter in a process of learning the artificial neural network.

Machine learning may be classified into supervised learning, unsupervised learning, and reinforcement learning.

Supervised learning refers to a method of training an artificial neural network with a label given for training data, wherein the label may indicate a correct answer (or result value) that the artificial neural network needs to infer when the training data is input to the artificial neural network. Unsupervised learning may refer to a method of training an artificial neural network without a label given for training data. Reinforcement learning may refer to a training method for training an agent defined in an environment to choose an action or a sequence of actions to maximize a cumulative reward in each state.

Machine learning implemented with a deep neural network (DNN) including a plurality of hidden layers among artificial neural networks is referred to as deep learning, and deep learning is part of machine learning. Hereinafter, machine learning is construed as including deep learning.

The foregoing technical features may be applied to wireless communication of a robot.

Robots may refer to machinery that automatically process or operate a given task with own ability thereof. In particular, a robot having a function of recognizing an environment and autonomously making a judgment to perform an operation may be referred to as an intelligent robot.

Robots may be classified into industrial, medical, household, military robots and the like according uses or fields. A robot may include an actuator or a driver including a motor to perform various physical operations, such as moving a robot joint. In addition, a movable robot may include a wheel, a brake, a propeller, and the like in a driver to run on the ground or fly in the air through the driver.

The foregoing technical features may be applied to a device supporting extended reality.

Extended reality collectively refers to virtual reality (VR), augmented reality (AR), and mixed reality (MR). VR technology is a computer graphic technology of providing a real-world object and background only in a CG image, AR technology is a computer graphic technology of providing a virtual CG image on a real object image, and MR technology is a computer graphic technology of providing virtual objects mixed and combined with the real world.

MR technology is similar to AR technology in that a real object and a virtual object are displayed together. However, a virtual object is used as a supplement to a real object in AR technology, whereas a virtual object and a real object are used as equal statuses in MR technology.

XR technology may be applied to a head-mount display (HIVID), a head-up display (HUD), a mobile phone, a tablet PC, a laptop computer, a desktop computer, a TV, digital signage, and the like. A device to which XR technology is applied may be referred to as an XR device.

The claims recited in the present specification may be combined in a variety of ways. For example, the technical features of the method claims of the present specification may be combined to be implemented as a device, and the technical features of the device claims of the present specification may be combined to be implemented by a method. In addition, the technical characteristics of the method claim of the present specification and the technical characteristics of the device claim may be combined to be implemented as a device, and the technical characteristics of the method claim of the present specification and the technical characteristics of the device claim may be combined to be implemented by a method. 

1. A method in a wireless local area network (WLAN) system, the method comprising: receiving, by a first serving access point (AP), a trigger frame from a served AP; transmitting, by the first serving AP, a Null Data Packet (NDP) request frame to a first station STA; receiving, by the first serving AP, a first NDP frame from the first STA and a second NDP frame from a second STA; receiving, by the first serving AP, a feedback request frame from the second type AP; and transmitting, by the first serving AP, an NDP feedback frame to the second type AP based on the first and second NDP frames.
 2. The method of claim 1, further comprising: receiving, by the first serving AP, a selection frame from the served AP; and transmitting, by the first serving AP, first data to the first STA and second data to the second STA.
 3. The method of claim 1, wherein the first STA is associated with the first serving AP, and the second STA is associated with a second serving AP.
 4. The method of claim 3, wherein the trigger frame includes information related to addresses of the first and second STAs, information related to a basic service set (BSS) to which the first and second STAs belong, and information related to an address of a serving AP to which the first and second STAs are associated.
 5. The method of claim 3, wherein the NDP request frame includes information related to the first serving AP and the second serving AP that will receive the first and second NDP frames.
 6. The method of claim 1, wherein the NDP feedback frame includes information related to a channel estimation value between the first serving AP and the first STA and information related to a channel estimation value between the first serving AP and the second STA.
 7. The method of claim 2, wherein the selection frame includes at least one of information related to an antenna, information related to a stream, information related to a Modulation and Coding Scheme (MCS), and information related to a physical service data unit (PSDU) length.
 8. The method of claim 2, further comprising: receiving, by the first serving AP, the first data and the second data together with the selection frame from the served AP.
 9. A first serving AP in a Wireless Local Area Network system, the first serving AP comprising: a memory; a transceiver; and a processor operatively connected to the memory and the transceiver, wherein the processor is configured to: receive a trigger frame from a served AP; transmit a Null Data Packet (NDP) request frame to a first station STA; receive a first NDP frame from the first STA; receive a second NDP frame from a second STA; receive a feedback request frame from the served AP; and transmit an NDP feedback frame to the served AP based on the first and second NDP frames.
 10. The first serving AP of claim 9, wherein the processor is further configured to: receive a selection frame from the served AP; and transmit first data to the first STA and second data to the second STA.
 11. The first serving AP of claim 9, wherein the first STA is associated with the first serving AP, and the second STA is associated with the second serving AP.
 12. The first serving AP of claim 11, wherein the trigger frame includes information related to addresses of the first and second STAs, information related to a basic service set (BSS) to which the first and second STAs belong, and information related to an address of a serving AP to which the first and second STAs are associated.
 13. The first serving AP of claim 11, wherein the NDP request frame includes information related to the first serving AP and the second serving AP that will receive the first and second NDP frames.
 14. The first serving AP of claim 9, wherein the NDP feedback frame includes information related to a channel estimation value between the first serving AP and the first STA and information related to a channel estimation value between the first serving AP and the second STA.
 15. The first serving AP of claim 10, wherein the selection frame includes at least one of information related to an antenna, information related to a stream, information related to a Modulation and Coding Scheme (MCS), and information related to a physical service data unit (PSDU) length.
 16. The first serving AP of claim 10, wherein the processor is further configured to: receive the first data and the second data together with the selection frame from the served AP. 17-20. (canceled) 